Cool Blue Hair Color For Dark Hair Ideas. Shade is one of the most important things to consider in your hair dye. Blue dyes can range from dark, inky blues all the way to pastel baby blues.

If your hair isn't lightened before you apply the blue hair dye, the color may not look as intense and vibrant as you were hoping. Bleach your hair for bright, vibrant color, or skip bleaching in favor of subtle results that are more akin to a dark. Here's how to pick your perfect blue hair hue.