I've done this, it can be a real pain in the ass. Not to mention the fumes. I had to do several layers over black and it still.came.out darker than I wanted.
This is usually going to be the case when painting over black, unless you're using really fancy paints. It's usually better to paint it white first before your color of choice
If possible, try doing filament swaps at a specific layer to make the colors blend in better. It can be a pain with a single spool printer but if you're willing to splurge a little more on a Bambu Labs model with AMS system you'll have a much easier time accomplishing this.