Question 1096509
There are 6 colors to choose from for the first
Each of those has 6 possibilities for the second in the group, since repetition is allowed.  That is 6*6=36
Each of those has 6 possibilities for the third, which is 6*6*6=216
and each of those has 6 possibilities for the fourth.
This is 6^4 or 1296.
A tree diagram for one color would show the fourth power and that would be multiplied by 4.