I'm posting this, as I didn't find anything similar, just to share my experience.
I'm using fluorescent acrylic colours from Daler-Rowney for my engravings inlay. I stroke the colour from all four directions into the engravings with mixed results. After drying the colour I scratched away the rests with a fingernail and took some colour out of the engravings.
Aceton works better as you can see on the backpanel.
I'll apply the colour a second time then it should work.
Regards,
Uli
Final result, I filled the missing pieces with a bristle brush. This works much better than a hair brush. Then I removed the protruding colour with a credit card and cleaned everything with Aceton.