1. A MPQ extractor with access to the ListFiles for the WC3 data archives.
2. A program that allows you to convert .blp files into a standard image format and back again.
3. A decent image editor that can let you recolour.
1. Extract the .blp textures used by the abilities from the data mpq's.
2. Convert them to a standard file formt (like tga jpeg depending on their compression type).
3. Use image editing software to alter their colours.
4. Convert them back to .blp files (remember to regenerate mipmaps if they were present) and use the same sort of storage (jpeg, pallet or bitmap).
5. Import them over the exact same path that the ability models use (where you got the texture from).