You could always use the red/blue variants of the skins. Some skins also have multiple colour schemes that you can use (e.g. green Proxy, white Proxy)
As an example, here's a skin using only 's'. The arms/torso uses green ("normal") Proxy, while the legs/helmet uses blue Proxy.
Alternatively, you could use different colours. 'b' and 's' are both shades of blue.