Actually, that proves color is the triangle in a weakness-strength pattern. So far the bottom color has always matched the larger color of the person your attacking whenever there's been an advantage. If you actually go and look through each pic, swords are red-green, red being weakness, green being strength, bow is green-blue, and the naginata shown in the January direct was Blue-red, getting an advantage on a sword which is once again, red-green.
EDIT: Aaand I get ninja'd by simple yet effective explanation. Ahh well, it further concreates what I've been pointing out XD