Sometimes simple vocabulary such as colors can be more difficult to remember than other vocabulary. One trick that I find useful, especially with adjectives, is to remember the color as it describes something. For example, if you can remember "un chat blanc" and picture a white cat, it is easy to remember. Of course, remembering a blue chicken is not going to help, so try to use combinations that you will likely see in real life. Here are a few suggestions:
un pomme rouge -- a red apple
un orange orange -- an orange orange
le soleil jaune -- yellow sunlight
l'herbe verte -- green grass
le ciel bleu -- the blue sky
une robe violette -- a purple dress
un style noir -- a black pen
un chat blanc -- a white cat
un chien gris -- a grey dog
un arbre marron -- a brown tree