Will potatoes turn brown / gray in oil?
Yes, it's oxidation, so yes, oil will stop it happening. However, broiling the potatoes straight from the oil will not yield very good results. You are much better off par-boiling them for 3 or 4 minutes, draining them, leaving them to steam and dry out for a few minutes, then coating them in oil and seasoning, and baking them for 30-45 mins. This will yield a nice, crispy-on-the-outside-fluffy-on-the-inside result.

So, if you're boiling them you might as well put them straight in the water you're going to use to do that.