I'm really loving a purple colour scheme for Lizards at the moment, that Slann looks lush.
As for scales (assuming you meant for the rest of the army) I'd be tempted to go for carmine, or a similar colour? Not a primary red, but one leaning towards the purple, even pink, side of the spectrum. Out of my other thoughts, that would be the one the most appeals to me.
The other options that went through my head were a purpler-blue mix such as Indigo (the highlights give it a warm colouration, so I'd personally avoid any more explicit cold colours unless it's on the equipment/base..that being said I'm curious as to how a icey-blue sail would look on Skinks), yellow (although the contrast could make it somewhat garish, it would look fairly tropical and reminiscent of a toxic frog) or either a very deep or a light pinkish purple