Club colours are determined by the text colours set in the editor, so the easiest thing to do is change the colours in the editor before starting a new save game, if you have started a game you'd need to use the IGE. Through skinning you can sort of change the colours but it would affect any teams using the same colour. From the settings.fmf extract the following three files and copy them into the settings folder for your skin; sidebar colours, accent colours, dark accent colours.