Since the French colours are RED, WHITE and BLUE in Enlgish, they are ROUGE (red), BLANC(white) and BLEU(blue)
You can't as red is a primary colour and you can't make any of the primary colours out of any other colours ( yellow, blue, red )
On their flag the colors are red, white and blue.
masc sing. / fem sing. / masc plural / fem plural purple violet violette violets violettes blue bleu bleue bleus bleues green vert verte verts vertes yellow jaune jaune jaunes jaunes orange...