Some cosmetics companies like Prescriptives have divided their shades up for you to make it easier to pick, and if you visit one of their counters, they'll work out the shades that will suit you best.

All Skin Tones: True primary red - ie. The classic London Bus colour. Although some argue that true reds still work best on pale skins.

Cool Skin Tones (pink undertones): Pink tones of red, Berry Reds, Blackberry Reds, Brick Reds, Blue tones of Red, Plum tones.

Warm Skin Tones (yellow undertones): Orangey reds, Warm reds, Tomato reds, Brown based reds, Golden reds, Tawny reds.

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Finally, it's worth mentioning that blue toned reds will have a whitening effect on teeth.