Tutorial: Two Tone Paint
In a modifying world where wackiness is the key to success, a standard single tone paintjob will not suffice! So here are the instructions to create two tone paint.
 Two Tone Paint
Difficulty - ***
With this car, we shall attempt to colour the bottom half blue.  
Draw around the area you want colouring with the lasso tool (L) and then copy (Ctrl+C) and paste (Ctrl+V) it.  

Now hit Ctrl+Shift+U to desaturate it. Then go to Image>adjust>variations. This allows to you to add colour.. All you have to do is click on the appropriate colour as many time as you like to increase the intensity. Or, you can mix colours like red and yellow to create gold. But here, I've gone for blue.  

You cant see it all too well on the above picture, but we have also coloured in the vents on the bumper in blue as well. Which we don't want! So just use the lasso tool, select and delete those areas using the delete key. We are now done. You should complete the picture by hitting Ctrl+Shift+E to flatten the new layer you made.