For when you want to wear a T shirt this might fit the bill perfectly. There are several colors available

You may need to shorten it. I think black or navy would be best to help hide it under the kilt. They come in tow neck types. I have not tried this yet but I am thinking about it. I don't know how it might affect the feel and swing of the kilt.

http://www.vermontcountrystore.com/j...erID=76&KICKER