There are many interesting colour-related expressions in French, some of which have different meanings to their English equivalents.
White or blanc, which also means pale or blank, can signify that something is without risks – à blanc – and that it is pure – blanc comme neige (white as snow). It is also used to refer to novices – des blancs becs (the white beaks) – and to refer to linen, as in magasin de blanc (linen/whites shop). If you are very frightened you might turn white as a sheet, but in French you turn white as a packet of aspirins – blanc comme un cachet d’aspirine.
Black is associated with illegal activity such as blackmarketering, or faire du marché noir, and moonlighting or travailler au noir. A black novel or roman noir is the equivalent of a crime novel, and when you want to be sure or something, you ask for it to be put down in black and white, or noir sur blanc.
In French you can go red with emotion – rouge d’émotion – or embarrassment – devenir rouge comme un cerise (to go as red as a cherry). If you stay out in the sun too long you might go as red as poppy, a peony, a crayfish or a tomato – rouge comme un coquelicot, une pivoine, une écrevisse, une tomate.
You might also go blue with rage – bleu de colère – or green with fear – vert de peur.