Even if I want the bow one solid color, I usually dye a shade darker than I want, then steel wool some of it back off. It lightens it a little, or a lot, depending on how much rubbing you do, but leaves the dye down in the grain and spring wood, which really brings the wood to life.
This seems to work a little better with aniline dyes than stains.
When I posted above, I was thinking you wanted to blend colors, but if all you want to do is 'fade' from dark to light and not 'blend' different colors, just dye it one dark color, then steel wool it to fade it to a lighter color.
Keep in mind, the more you rub, the lighter it's gonna get... so I usually do this thing where my strokes with the steel wool start small with moderate pressure and gradually get longer with less pressure.... which in the end will help fade light to dark.
Either way, steel wool is the ticket.