As the April birthstone, diamonds are the ideal gift for a loved one. And now you have more choices than ever. Get creative and give the ultimate gift of beauty: a fancy-colour diamond. Fancy-colour diamonds are natural, rare and truly exotic gem of the earth. Diamonds in hues of yellow, red, pink, blue, and green range in intensity from faint to vivid and generally the more saturated the colour, the higher the value. In fact, diamonds sparkling with intense colour are rare and may be priced higher than a colourless diamond of equal size. Because fancy-colour diamonds are very desirable, colour is sometimes introduced in a laboratory. These are correctly called colour-treated diamonds. When purchasing a fancy-colour diamond, the shopper should ask if any enhancements or treatments were used to improve its colour and/or clarity.
Taken from http://www.americangemsociety.org