Teachers' Day balloons float in the air.

Then 84 divided by 6 is exactly 14, so there are 14 groups, one red, two yellow, three blue, and the 84th blue.

On the other hand, if you say the first red, the second yellow and the third blue, 83 divided by 3 equals 28, then the 84th is blue.

So in either case, the 84th colored ball is blue.