Bob's answer is a good one. In the first case, I would recommend removing the 'in's from the second sentence to make it less wordy. It does lose the parallelism with the first sentence, but I think that's acceptable in this case.
There are five items in four different colors. One is red, another is yellow,
another is green, and the others are black.
A better structure, in my opinion, works off of the second case:
There are five items in four different colors. Two of the items are black,
and the three others are yellow, blue, and green, respectively.
I think it's pretty clear what you're trying to say here, i.e. that the three remaining items correspond to the three remaining colours. I mean, if five items are in four colours, and you mention that two of them are black and list three other colours, it's pretty clear that this is the case.