<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>0011 - Disclosure - 4A. DEVELOPMENT OF SPECTRAL PATTERN MATCHING TECHNOLOGY</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

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</LabelSeparator><Level>1</Level><ElementName>VSUL_NotesToFinancialStatementsAbstract</ElementName><ElementPrefix>VSUL_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Notes to Financial Statements</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>VSUL_DevelopmentOfSpectralPatternMatchingTechnologyTextBlock</ElementName><ElementPrefix>VSUL_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="From2011-10-01to2012-09-30" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;The Company has developed a unique patented Visualant Spectral Pattern
Matching&amp;#153; &amp;#34;SPM&amp;#34; technology. This technology directs structured light onto a physical substance to capture a Visualant
Spectral Signature &amp;#153; called a ChromaID&amp;#153;. When matched against existing databases, the ChromaID can be used to identify,
detect, or diagnose markers invisible to the human eye. ChromaID scanners can be integrated into a variety of mobile or fixed-mount
form factors, making it possible to effectively conduct analyses in the field that could only previously be performed by large
and expensive lab-based tests.&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;Visualant Spectral Pattern Matching and the ChromaID profile were
developed over a seven year period by Professors Dr. Tom Furness and Dr. Brian Showngerdt of RATLab LLC under contract to Visualant.
The technology is now being transferred into products and a ScanHead module. Visualant has partnered with Sumitomo Precision Products
to manufacture the ScanHead and reduce the technology to a reliable and cost effective form. The first demonstration of this is
the Cyclops6 ChromaID Scanner which was demonstrated at the Japanese Instrumentation Manufacturing Association trade show in Tokyo
in October 2012. The Cyclops 6 ChromaID Scanner can be used to evaluate the technology for flat surface applications and has sensitivity
from 350nm to 1450nm.&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;Visualant is pursuing an aggressive patent strategy to expand our
unique intellectual property in the United States and Japan. The following patents have been issued to date:&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;On September 6, 2011, the Company announced that it was issued US
Patent No. 7,996,173, entitled &amp;#147;Method, Apparatus and Article to Facilitate Distributed Evaluation of Objects Using Electromagnetic
Energy,&amp;#148; by the United States Office of Patents and Trademarks.&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;On January 19, 2012, the Company announced that it was issued US
Patent No. 8,081,304, entitled &amp;#147;Method, Apparatus and Article to Facilitate Evaluation of Objects Using Electromagnetic Energy&amp;#148;
by the United States Office of Patents and Trademarks.&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;On March 20, 2012, the Company announced that it was issued US Patent
No. 8,076,630, entitled &amp;#147;System and Method of Evaluating an Object Using Electromagnetic Energy&amp;#148; by the United States
Office of Patents and Trademarks.&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;On November 1, 2012, the Company announced that it was issued US
Patent No. 8,285,510 entitled &amp;#147;System and Method of Evaluating an Object Using Electromagnetic Energy&amp;#148; by the United
States Office of Patents and Trademarks.&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;On June 7, 2011, the Company closed the acquisition of all Visualant
related assets of the RATLab LLC (&amp;#147;RATLab&amp;#148;). The RATLab is a Seattle based research and development laboratory created
by Dr. Tom Furness, founder and Director of the HITLab&amp;#160;International, with labs at Seattle, University of Canterbury in New
Zealand, and the University of Tasmania in Australia. With this acquisition, the Company consolidated all intellectual property
relating to the SPM technology except for environmental field of use. &amp;#160;The Company acquired the Visualant related assets
of the RATLab for (i) 1,000,000 shares of our common stock at closing valued at $0.20 per share, the price during the negotiation
of this agreement; (ii) $250,000 (paid); and (iii) &amp;#160;payment of the outstanding promissory note owing to Mr. Furness in the
amount of $65,000 with accrued interest of $24,675 (paid).&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;On July 31, 2012, the Company closed the acquisition of the environmental
field of use of its SPM technology from Javelin LLC (&amp;#147;Javelin&amp;#148;). The Company acquired the Visualant related assets
of Javelin for (i)&amp;#160;1,250,000 shares of our common stock at closing valued at thirteen ($0.13) per share, the price during
the negotiation of this agreement; and (ii)&amp;#160; $100,000, with $20,000 payable at closing and $80,000 to be paid in four equal
installments over a period of eight months. In addition, Company entered into a Business Development Agreement which will pay Javelin
ten percent (10%) on the gross margin received by Visualant from license agreements and joint venture developments sourced by Javelin.&lt;/p&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>No authoritative reference available.</ElementDefenition><ElementReferences>No definition available.</ElementReferences><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>4A. DEVELOPMENT OF SPECTRAL PATTERN MATCHING TECHNOLOGY</Label></Row></Rows><Footnotes /><IsEquityReport>false</IsEquityReport><ReportName>4A. DEVELOPMENT OF SPECTRAL PATTERN MATCHING TECHNOLOGY</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>true</HasCustomUnits><IsEmbedReport>false</IsEmbedReport><IsMultiCurrency>false</IsMultiCurrency><ReportType>Sheet</ReportType><RoleURI>http://visualant.net/role/A.DevelopmentOfSpectralPatternMatchingTechnology</RoleURI><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows></InstanceReport>
