Yes,subconscious thinking makes a simple user worry if the objects like folder tabs on a usual windows form are grey. Either they are "OFF" or "INACTIVE" or "NOT FOUND" - that's what comes to the mind first. Besides, in comparison with yellow ones, these are depressive. I don't think "The designer of this should be fired", I think he might get a good lesson. You have to be careful when changing things people are used to deal with.
I read formerly once airplane designers made a new comfortoble style of the cockpit. The pilot tried the simulator flight and liked it. But when the aircraft gained speed on the runway, it flopped the fuselage against the ground instead of taking off. The reason was that the designers had built the lever of the landing gear at the place where the control lever flap is usually found. They have made one more try to fly with the same result. The pilot trained without mistakes but when he sat in a real plane, the habit became in power. It's mankind thinking, it's human psychology and you have to take it into consideration.