The problem is, there were really no standard colors at that time. Tartan colors differed according to the dyes the weavers could glean from native plant life and quite often the members of the same clan wore definite variations of color. My solution was to have my male character wear a specific plaid most of the time, but he does make an appearance in another tartan in one part of the novel. This probably won't sit well with purists of Scottish historicals. If not, they can write their own novels and educate me.
Celtic novels are a highly popular form of fiction.
Readers are devouring all the Celtic lore they can find and they are savvy about names, places, and history. This trend has given us many fine books on Celtic folklore and myths and legends. It also makes accurate research critical. Good history books on Ireland and Scotland are easy to find now, where several years ago such books had to be special ordered. Many authors keep research notes on 3x5 cards.