I wear cream-colored hose (and blue flashes) with my Shaw tartan because I could only afford one pair when I bought the kilt, and cream seemed like a good multi-occasion color. However, the easiest way to pick an actual color is to determine the dominant colors of the tartan. In our case, the blue and green are dominant, so either would be a good choice. I'm about to have a pair of blue, and will probably find some red flashes to go with them.