I second the motion from a couple of posts above about SWK.

I ordered, and just received, a black "shadow tartan" kilt in their heavyweight wool. Now, it's no tank, but I ordered it (and you state that you want) a casual wear kilt.

I couldn't suggest this kilt more. It looks great! It is jet black, so it matches my t-shirts, dress shirts, and even my Celtic jersey (GO HOOPS!). The kicker is this; when the light hits it, the "tartan" pattern comes out. It isn't a different color, it a weaving pattern, so the light reflects off of it differently, in a general plaid pattern.

Bottom line = It is wicked awesome!