1) Download the Recolour Template for your favourite object from the threads in this forum (if the template image is packed into a zip or rar archive, extract it and put it in a working folder - NOT in the Downloads ).

2) Edit the template image using any paint program.

3) Follow THIS TUTORIAL that explains how to create a recolour package; when the tutorial asks you to import the new image in the package, import the image that you have edited earlier.