Well first thought would be depending on what the alpha legion are fighting, other legions might result in altered paint schemes such as ultramarines and whatnot.

Apart from that I've always liked the teal green/ mable blue/green color scheme that some of the ones I've seen if your after for advice for paints currently thinking screamer pink and one of the lighter greens might result in that marble color, not too sure of a ratio to get it to look good proably someone else might have some advice.

Thats all i got