Not all models can deal with the changing of colour schemes for the maps. If yours can, under Preferences, is Change Map Colours active? If so, yours should be able to handle them.
You should be able to cycle through the choices and you should see an 'advanced' button where, if selected, you can scroll through the choices you have. The custom ones you dowloaded, though, will appear as a rainbow icon (sort of) and you'll only see how it looks once you selected it.
This all assumes the schemes are in proper format and have an extension of .clr on the files.