[BD]

Extract pak0 and go into the folder called ui. In there find the files names hud_ammo_gun.urc, when gun is the name of the gun. There's a line in each section of the files that looks like "fgcolor 1.00 1.00 1.00 1.00" but with different numbers. The numbers are percentages of the three primary colors. 1.00 is 100%, 0.00 is 0%. Feel free to mix and match to get the color you want. The numbers, in order, mean red, green, blue and alpha (transparency). The higher the number, the more vibrant the color. In terms of the alpha channel, the lower the number, the clearer it will be.

If you want to continue editing the colors, open hud_health, hud_score, and any other file that starts with hud_ and change the colors to what you want.

I hope that was of use.