without reading your other post, I guess that your new sheltie is a merle...
merles frequently have blue eyes or spots of blue in the brown eye...
the eyes will stay blue/brown and there's no health issues related to that.
I have 2 shelties with one blue/one brown eye (it's called heterochromia and also occurs in people, cats, etc). I had one in a pet store years ago and a kid asked if he could see out of the blue eye- I'm like people can see out of their blue eyes, why would you think that a dog couldn't see because the eye was blue.