Here's an easy way to color the engravings on your blued steel gun slide. It's cheap and easily removed. The wax from melted crayons will fill in the engravings and add some 'pop' to you gun. If you don't like it, you can heat up the slide and remove the wax with a cloth or paper towel.

I like this method over enamel or nail polish because it's fool-proof.
If you get sloppy, no problem - just heat it up and wipe it clean.
If you want to sell the gun - just heat and wipe.
If you want a new color - heat and wipe and re-apply.

Step 1: Required Materials

The materials required are:
Crayon(s) - you can experiment with different colors, I chose white and grey
Lighter
Stiff paper (I like playing cards)
Notebook or newspaper

Step 2: Field Strip Gun

MAKE SURE YOU FIREARM IS UNLOADED!!!!!

CHECK IT AGAIN!!!!!!

Remove all cartridges from the room and field strip the firearm. Consult your manual for exact procedure.

Step 3: Apply Wax

Heat the slide using the lighter, being careful not to get any soot onto the slide. It's best to keep the lighter 1" from the surface. It won't take too much time to heat it up. Just heat the area to apply color so it's warm enough to melt the crayon. When it's hot, liberally apply the crayon, any color you like, making sure to fill in all of the engraving. It should completely cover the engraving. By heating the slide it will flow and adhere to the metal.

Step 4: Cool the Wax

Stick it in the freezer for fifteen minutes or more. This will solidify the wax. The slide will cool slowly from convection and will not warp.

Step 5: Remove Excess

Remove the slide from the freezer. Heat in up with the lighter (not too hot) again to melt the surface wax. Now using your stiff paper, scrape the excess off the slide. Don't use a rag or anything with loose fibers as these will remove wax from the grooves of the engraving.

Use the loose newspaper to rub off the excess after scraping. The frictions from rubbing the newspaper should be enough to heat up the wax and rub it free.

You can now clean the gun as normal using any standard cleaner (e.g. Hoppe's 9, Breakfree CLP) without worry.

Step 6: Take It to the Range and Let It Loose!

Reassembly your firearm and enjoy!

I've fired 300 rounds since coloring without any wear to the wax.

If at any time you want to change the color or go back to bland, just heat it up and remove the wax with a soft towel.