I've been doing a bit of number crunching. The 99.8% confidence intervals for the average numbers of different colours per tube are:
Black: 2.452 - 2.623
Red: 2.923 - 3.267
Orange: 2.894 - 3.117
Yellow: 2.764 - 3.210
Green: 2.229 - 2.521
So basically, there's a one-in-500 chance that the average for green is above 2.5.
For the mean to be 2.8, the Z value (normal distribution) would need to be 8.9, which is more than twice as big as any that I can find the tables. (The highest I can find is 3.99 and that corresponds to a one-in-nearly-17000 chance). When I calculated the value for 8.9 myself, it came out with something like a 1-in-1500000000000000000 chance.
I'm not 100% sure the last calculation was correct but, basically,
it's pretty unlikely that green's average is anywhere near where it should be.