[Death by Mirrors]

Alright, now I'm confused. Granted, guessing green was a goof on my part (it was already late at my place and only when I checked the instructions again today I realized green was just part of the firewall colors, not the code itself). So from my previous attempts I'm fairly certain it has to look like "something something something blue" and there is a purple and a yellow in there also, at locations which still have to be determined.

The fourth color obviously isn't green, as there is no green. However, if the fourth color was red, the first try would have 3 colors correct (red, blue and yellow). So no red. Same if the fourth color was yellow (blue, yellow, yellow). So no yellow either. Now if the fourth color was blue, the second try would have all four colors correct instead of three. Therefore no blue. But if the fourth color was purple, the fourth try would have all four correct, so it can't be purple either. Is something like "nothing" or "empty" a valid color?

In that case I'll try: empty yellow purple blue.