I tested with Digital Color meter and I get 255 everywhere.(OSX 10.14.3)
It does not appear to be a major issue.Noone will ever be able to see the difference. But from a computer program perspective, I imagine that could create problem if you are comparing colors.
Did you test with other colors like 128,128,128
Could it be a problem in ColorMeter ?
I confirm the issue with Digital Color Meter and another pixel color sampler. I suspect the problem is with the samplers and their math. If you take a screenshot of a TextView and flood-fill it in an image editor the whole view fills (there are no off-pixels that stick out).