I'm not sure about this...but I'll take a stab at it
The probability of red or black = 18/38 = 9/19
And the probability of green = 2/38 = 1/19
So the probability of a ball landing in red 4 times = (9/19)^4
And the probability of a ball landing in black twice is (9/19)^2
And the probability of landing in green once is (1/19)
And note that we have 7! arrangements of these results......but some are indistiguishable from others
So, the totlal distinguishable arrangements is 7! / [4! 2! ] = 105
So the total probability is given by.... 105*(9/19)^4*(9/19)^2*(1/19) = 0.0624265233650037 = about 6.2%
