My trews are always cut in MacMillan Hunting tartan, modern colours. My kilts run the whole spectrum of tartans and colours-- my newest (thank you, Barbara Tewksbury) is in Ancient MacMillan modern colours and my next will be in MacMillan Hunting, ancient weathered colours. Because trews are most often worn in the evening I prefer the look of a darker tartan, hence the modern colours. As Heath has pointed out, there is no reason not to have the trews and the kilt in the same tartan other than personal preference.

Proper trews are high waisted and cut snug in the leg (although full in the seat). They also only have an inner seam which allows the tartan to "match up" on the outside of the leg. Before parting with your hard earned cash, be sure your tailor is making proper trews, not tartan trousers.