I don't think the shifter can control the color of its eyes but instead they are naturally that way. And also, each shifter has a different eye color when in other form; Vidar's eyes are emerald green, Penelope's are silvery green, Alberich's are bright blue and Bran's are dark gray.
Where did you get that from? If you think that Vidar is the one with the emerald eyes, then Vidar was in 2 episodes because the shifter with the emerald green eyes appears only in 2 episodes. Penelope, the shifter with the silvery green eyes appears in more episodes. Do you have any proof that it was actually Vidar who killed Bill Thatcher, or the shifter in 1x03 was really Vidar and not Penelope?
Will it have 3 season??? I really want to enjoy one more seaon but I was really sad, because my favourite hero - Wendy died but I dont know did she really die or her "sister" - Helena will help her to get back to her family. I will be really happy to see her alive.