Bulls and Cows

Frank and Joe are playing a game of Bulls and Cows. Frank has thought of a sequence of 4 colors. Joe is trying to guess that sequence. The color choices are Red, Orange, Yellow, Green, Blue and Purple. After each guess that Joe makes, Frank tells him how many Bulls and Cows he has. A Bull means that Joe has the right color in the right position.  A Cow means that Joe has the right color but it is in the wrong position. Below is how the game has gone so far. Can you tell what Joe should guess next to win the game?