The pattern suggests a combination of intarsia (for the larger areas of color B) and fair isle or stranded knitting (for the small number of color B sts). Even if it's 5 or 10 sts of color A, it would be better and I think, give you a better finished piece to strand the contrast color along the back of the main color here. Since this is meant to hang on a wall, you can probably strand over 5sts and in areas with more sts, catch the yarn at intervals. See the video
for tips on fair isle/stranded knitting. And please, could we see this when finished if you care to post a photo? It's going to be spectacular.