I've had a leather bag redyed its original color at a shoe repair shop. It only cost me $30 or $35 dollars. But, if you want to dye your bag a completely different color I'm sure a shoe repair shop could do that as well.
Do you have to be careful about the dye bleeding in the rain or rubbing off on different-colored items (say, a redyed black purse with a white jacket)?
If you read Icy's post from I DYED my MAM! Come check it out! She says that she got caught in the rain and the water beaded right off. The tarrago website even says that it puts a protectant on your bag too with the dye.
I ordered it. It was 10.79 with shipping. It should be here late this upcoming week. I plan on testing it on a cheaper bag that I have first and if it works well, then I am going to be making the Cole Haan the stone color I have been dreaming of!
A good leather dye can never go from dark to light. Much like hair color, you cannot go lighter without bleaching the leather first.
Now, you can coat a bag with a different color, but that's not the same thing. To actually dye the leather and change the color of the leather fibers, you can only go darker unless a very experienced person does the work.