This is a ColdFusion 10-only UDF that will identify whether a JPEG image is a CMYK or not.

isImageCMYK UDF

<!---   isImageCMYK() v1 (7/6/2013)
    UDF for ColdFusion 10 by James Moberg
    Identifies whether a JPEG image uses a CMYK (CUSTOM) palette
--->
 
<CFSET ImageFile = expandPath("cmyk.jpg")>
<CFSET ImageObject = ImageRead(ImageFile)>
 
<CFOUTPUT>
File = #isImageCMYK(Imagefile)#<br>
File = #isImageCMYK(ImageObject )#<br>
</CFOUTPUT>
 
<cffunction name="isImageCMYK" returntype="boolean" output="false" hint="Returns a true/false indicator regarding if image uses CMYK (CUSTOM) palette.">
    <cfargument name="image" default="" required="true" hint="path w/file or image object" />
    <CFSET local.testImage = "">
    <CFSET local.isCMYK = 0>
    <CFIF IsSimpleValue(arguments.image)>
        <CFIF FileExists(arguments.image) AND IsImageFile(arguments.image)>
      <CFSET local.testImage = ImageRead(arguments.image) />
    </CFIF>
    <CFELSEIF isImage(arguments.image)>
        <CFSET local.testImage = arguments.image />
    </CFIF>
    <CFIF isImage(local.testImage)>
        <CFIF NOT val(imageGetBufferedImage(local.testImage).getType())>
            <CFSET local.isCMYK = 1 />
        </CFIF>
    </CFIF>
    <cfreturn local.isCMYK />      
</cffunction>