<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2025-06-30</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0002063816</issuerCik>
        <issuerName>Indigo Acquisition Corp.</issuerName>
        <issuerTradingSymbol>INACU</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001036796</rptOwnerCik>
            <rptOwnerName>CASSEL JAMES S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE ALHAMBRA PLAZA</rptOwnerStreet1>
            <rptOwnerStreet2>STE 1410</rptOwnerStreet2>
            <rptOwnerCity>CORAL GABLES</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33134</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Ordinary Shares</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2214286</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Indigo Sponsor Group, LLC</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Rights</value>
                <footnoteId id="F3"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
                <footnoteId id="F3"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Ordinary  Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>22929</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Indigo Sponsor Group, LLC</value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes 229,286 shares contained within units that Indigo Sponsor Group, LLC purchased in connection with the Issuer's initial public offering (&quot;IPO&quot;).</footnote>
        <footnote id="F2">These securities are owned directly by Indigo Sponsor Group, LLC of which Mr. Cassel is a managing member.  Accordingly, Mr. Cassel is deemed to be the beneficial owner of such securities.  Mr. Cassel disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.</footnote>
        <footnote id="F3">Represents rights contained within units that Indigo Sponsor Group, LLC purchased in connection with the IPO as described in footnote 1.  Each right will convert automatically into 1/10 of one ordinary share at the closing of an initial business combination by the Issuer.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ James S. Cassel</signatureName>
        <signatureDate>2025-07-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
