First, basecoat your boys with black spray paint.
Second, paint the pants and the shirt Calthan Brown and wash them using Devlan Mud (Nuln Oill) wash.
Drybrush them with Khemri Brown and then with Dheneb Stone.
Third, paint the strips on the clothing Dheneb Stone and wash ‘em using Devlan Mud(Nuln Oill).
Now you need to paint the Ork skin using any really dark green you like. After you did it highlight the skin with green paint which is slightly lighter than the dark green you were using. Then, highlight it with light green and wash the skin using Thraka Green Wash.
Paint the skulls, nails and the teeth Dheneb Stone and wash 'em with Gryphone Sepia.paint the eyes and the tongue red.
So this is how the finished Ork Boy looks like!