Laser etching is a great process but I've often wished I could have higher contrast etched text, colors, etc. Then I realized I could do that very easily. If you're laser etching acrylic sheet it already comes with a protective paper covering which makes an awesome paint mask.
So the basic process is deeply laser etch the panel with the protective paper in place. Paint though this protective paper mask. You can be as sloppy as you like. Then simply peal the paper away. Now you have super clean highly detailed etchings, and the paint is protected because it's actually recessed into the plastic. (That's why you use a deep etch.) You can use any color or combination of colors you like.
Step 1: Deeply etch the design with a surface mask in place.
Do a deep laser etch of your design on acrylic with the protective paper in place. I suppose you could also try this by pre-masking non acrylic object. Like putting contact paper on wood, etc. But I haven't tried it and I'm not certain we're allowed to vaporize contact paper in the laser I have access to.
Step 2: Paint the parts of the design
Now you can paint the various parts of the design. I use standard art acrylic paint. High contrast uniform colors work the best. I've tried metallic colors as well, but those are more sensitive to stroke direction, evenness, etc. So they won't look as professional. (Although I've had some nice effects using that technique.) You don't have to paint carefully, just make sure you get the colors down into all the nooks and crannies.
You can use any color you like, and paint different areas different colors, etc. Here you can see me making a set of gear dials with different colored accent lines. I'm sorry this doesn't match the previous image of what I was laser etching. I wasn't originally trying to document this process, so I didn't take a picture of every step. Jim said I should make an instruactable about it though, so I am, minus the original laser etching/cutting image.