It’s allways the same Colors coming as reward.
As exemple i take Jean Grey 4*… your cover Color as reward are blue, and then violet… and where are the green one ??? In the next Event you have the possibility to win a Jean Grey cover… oh what a surprise, a blue one…
Since a very Long time i have 5 blue and 5 violet… no wax to have the green one (I have just one)
and for other caracters it’s the same… like Hulk Amadeus Cho and his green cover…