The pics were meant to illustrate the effects of using tap water, not to answer the question about brass barbs. The green is definitely lime scales, not verdigris.
The difference between water lines and water
blocks is that one is being used for heat transfer and the other isn't. Even if a small layer of lime forms in a block, what do you think that's going to do to heat transfer?
Here's a copper household pipe that has significant lime buildup.
