While I do make sure I wear a solid shirt with my tartans I do have a bit of leverage with a solid color kilt. I bought a saffron colour kilt for this reason. My favorite, old, comfy, cozy winter flannel shirts have the large plaid so I was sort of bumming at not really thinking they would go well with the tartans. They do go well done casual with the saffron kilt. Im sure even the Irish green or black would look nice but my cats shed to much for me to even think about black. Photo is proof.

Saffron Kilt with white and black plaid flannel shirt.





I sometimes do have to check with my gf about what colour skirt she may have on and if she is dressing up or not, but that is small issues with us. And yes tan or khaki would go well with your blackwatch, Id wear the same combo too.