Double-click the Gantt bar and then change the color in the Format Bar dialog.

@ Dale Howard
Thanks for an answer, but the question is whether there is a standard way to get a different color of the bar for a certain task.

Your proposal is to adjust the task afterwards, the question was to be able to define this in advance.

So I see the answer as placing buckets near a leaky faucet, instead of fixing the faucet.