Well, in order to take your dark hair light, you need to lift the dark out, which means bleaching, then depositing your desired color. My hair is naturaly dark brown, and I color it ash blonde, which requires bleach- my hair is pretty resistant, so I have to use a 40 volume lift, but usually it's not recommeded to use that high of a lift. 30 is the standard, but it only takes my hair to a bright gold which taints the final result. Since the contrast is extreme between the blonde and the natural color, touch ups on the new growth is pretty quick (unless you're lazy like ME and let more than an inch grow out before getting around to it!!)
Just remember, the lighter shades are VERY high maintenence, you have the double processing on your hair (which BURNS, by the way!), the conditioning you already have with black hair is more with the color treated hair, because you have stripped it down by this point with the bleache. Then you have your daily conditionig to keep the moisture in, and products to keep the color bright and resist fading.
I love my color, and have done this for years, but it is tedious work, so I spend much time with braided extensions, so I don't have to bother with my own hair for a while.