Just found this list which is handy not sure if its been posted. If anyone wants a color but can't get it due to being locked you can use this. It's a list from a file of all the official colors in the game.
Take the 2nd, 3rd and 4th numbers in the brackets and use them in a color swatch. It's the RGB combo or you can use the last 6 digits in the 0xFF code.
For instance Lime is a locked color but using this.
LIME_GREEN = 0xFF568F00 (255, 86, 143, 0)
Outputs : #568F00 (http://www.color-hex.com/color/568f00)
Pretty handy since you can do pretty much everything, I've just used it on my Adder for brushed gold since i haven't reached rank 100 and it's identical you can use all shade of the silver metal to make a dark gold or bright version. The metal effects aren't identical but the classic, matt or metallic are.
Its also cool if you want a certain color already in-game but in the matt version, or say you like the color but want it to be a little more stronger or weaker in color. Just take the color into photoshop and increase/decrease saturation it by 10% and use the new code.
I'm going to test around with some colors see if I can make any cool ones. I took one of the default browns and increased the red saturation in Photoshop then took the new code. Looks more what I wanted.