The GIMP XCF Templates can be used to simplify the creation of new skins. Each layer in the template identifies a specific filename that is used to save that image. Each one has to be extracted manually, but the templates are fairly accurate in positioning so that you can work on the "IMAGE_" layers and then you can open the specific filenames identified by the layers, copy and paste from the template, and then select "Save As..." and save it under the same name. You select save as so that you can go into the "Advanced Options" and select R5 G6 B5 as the bitmap format.

Here are some shared skins. Feel free to create your own and share it. Click on the picture to see it full size, or click on the link under the picture to download the .ZIP skin that can be used in IomTools.