I used to have a 3 pin vital bow gear sight that had all green pins. I don't see where it would cause confusion as long as you dont associate color with yardage. I always would just count from the top, top pin is 20, 2nd is 30, and 3rd is 40 yards. If you think of it in this way, you shouldn't get confused by it.

Also I believe it was Greg who said that he uses the brightest pin at 20 the 2nd brightest color at 30 and the dullest at 40. So in low light they dim out in reverse order 40-30-20. To discourage taking a low percentage shot at a long range in low light.