Why is o left out

Hi, let's see if we can put the one orange car in 3. _ _ O _ _ _ Since we know four cannot be orange or green, it must be purple. Additionally we know that one of five and six must be purple, and it cannot be five since we cannot have two purples next to each other _ _ O P _ P However, this would force greens next to each other in one and two, so O cannot be in 3.