There's a possible contrast here. Rhaegar in red and black, Lyanna in blue and white. White and black are real life opposites, while red and blue are thematic opposites in ASoIaF, so the grouping of these four colors caught my eye, because they've been grouped elsewhere. Specifically, in Bran and Dany's chapters, except that it's red and white vs. black and blue; e.g., weirwoods vs. the trees the warlocks make shade of the evening from, which has black bark