Grey will always look good with any tartan and almost any event, and does double as a semi-dress jacket color for non-black tie dressy evening or day events. Personally grey/charcoal would be (and indeed was) my first non-barathea jacket/waistcoat purchase. Just about any other color tweed can be worn with just about any other tartan (within reason now guys) as remember the true highlander is not particularly worried about matchy-matchy things, at least not as much as many of us yanks, myself included. Personally I've also a nice light Lovat green tweed, midnight navy blue Harris tweed, and olive with navy box check Cheviot tweed jacket waistcoat sets, and am now looking for something in the brown or tan range to cover all the color palette bases, so to speak, that might look good with my various tartans in modern, ancient, muted, and weathered colorways.

Choose something in a color that you will feel comfortable wearing, and it should look fine with just about any tartan out there, so long as you wear it properly and with pride and confidence. Enjoy.

jeff