Get a white paint marker (a new one with a virgin tip is best), plastic handled cotton swabs (Walmart brand are good), a good clean shop rag, and some lacquer thinner.
Clean the area you want to high-lite with the thinner and let it dry thoroughly.
Then crack open the paint marker and get the paint flowing to the tip as per the instructions.
Next go over the engraving until the indentions are filled (You'll have to re-wet the paint marker tip per the instructions a few times to completely fill the engraving). And it doesnt matter if you get paint onto the finish of the lower in the design thats supposed to be the background color or around the edges of the design.
Now let the paint set up until its tackie to the touch and not completely dry.
Then get out your cotton swabs and get one end soaked in the thinner and start to gently whisk it over the painted area. The paint will smear once the thinner is applied, but thats no big deal.
You need to work slowly and use new swabs once you notice the paint building up on the one youre using.
You might also have to re-coat shallow parts of the engraving as the paint can be whisked out easily by wet swab. This isnt anything to get upset about, it happens no matter what you do, its just a matter of re-painting and working slowly.
Last you'll have to take a wet swab and go over the entire area to get the paint that was smeared over the anodizing as you cleaned the paint from the design area.
There you go, long hand, how I do it. It takes some time to get the hang of it, but once you learn the touch for the shallow places and how wet you need to get the swabs its all gravy from there.
Hope this helps.