As Noel said, drawing UI from scratch is tedious task. You don't want to do it unless you have 100-400 hours extra time for the project.
Been there, done that...
Instead of drawing everyting from scratch you can easily tweak colors in Photoshop or similar. To get started, import UI files to Photoshop, open Saturation: check [X] Colorize, then tweak hue. Add Levels layer etc. to finetune colors and maybe add some dirt. However, you have to be careful because money can't buy good taste:
Unofficial customizing