Using Catmg's combinations that do not appear to be in question
1, 1, 4, 6
1, 2, 2, 6
1, 2, 3, 4
2, 2, 2, 3
Assume all the dice are different in colour. (That will make it much easier)
Also assume that the dice are rolled one at a time. It is probably easier to act as if order counts.
That means they are all unique and a green 1 is different from a blue 1
The total number of combinations is 6^4=1296, just as catmg found.
Each of those 4 combinations above can be formed in 4! ways. But I do need to allow for the double counting here
1, 1, 4, 6 4!/2 = 12
1, 2, 2, 6 4!/2 =12
1, 2, 3, 4 4!=24
2, 2, 2, 3 4
total 52
So we have a prob of 52/1296 = 13/324
I am not 100% sure that this is correct ....... But it is the same as guest found so maybe it is ok.