There were probably some CS units which wore them with yellow trim but look at original pictures to see what was really being worn. The thing about a yellow trimmed kepi was that it usually would have to be bought from a supplier and not issued from a depot. The number of original kepis or "caps" that survived is very few. All enlisted kepis I have seen are very plain. Officers caps tend to be better quality and may be adorned with rank piping or colored trim. The exception (and there always are exceptions) would be a unit which was well supplied from other sources other than a government depot. An example of this would have been the Washington Artillery from New Orleans with their red trimmed kepis. Don't know what the Yanks were wearing but I suspect there are more Yellow trimmed kepis on Sutler row than were in either army.

I have some original US and CS kepis pictured on the show and tell site referenced below.