It's actually quite simple. I might make a quick video tutorial, but all I did was use the pen tool (selection mode) and select around the edge of the area I wanted to fill in, then I right clicked (with the pen tool still selected) and clicked make selection. Then I created a new layer, filled it with the colour I wanted then set the blending mode to colour. Then you need to get the smudge tool (with a average to small sized brush) and smudge out your colour layer until your happy with your paint job.
For the text all I did was type some text in black, then right clicked on it in the layer panel, click "Rasterize Layer". Then rotated and resized it to how I wanted it then set the opacity down until I was happy. Then I grabbed the pen tool and made a selection on the windows, where the wheels are etc. then I right clicked, made a selection then hit deleted so it deleted anything that was selected (in this case the excess font of "Kawasaki").
Might seem a bit complicated just reading it but it only takes a couple minutes lol.
Edit:
Paint Job Example Video - Metacafe
Didn't include the text part, but thats pretty straight forward.