Don't know how many colours you are using, but just off hand I think I would pull that green guy into a drawing program like ImageFX, or maybe even DPaint, then use a stencil (or a carefully defined region) so that the whitish colours aren't affected by any changes. Then just use the balance controls to tint the picture reddish and pull the green out - but the whitish colours (eyes, claws) shouldn't be affected.