The gray color in your microwaved russet potatoes is likely due to oxidation, which can happen when potatoes are exposed to air after being cut. This doesn’t mean they’re unsafe to eat, but it can affect the appearance and taste. Here are a few things to consider:

• Edibility: The potatoes are still edible as long as they don't have an off smell or texture (such as being mushy or rotten).
• Taste: Oxidation can sometimes cause a slightly off taste, but it shouldn't be harmful.
• Preventing Grayness: To prevent this in the future, you can soak cut potatoes in water for 10-15 minutes to reduce oxidation before cooking, or add a small amount of lemon juice or vinegar to the water.

So, if they seem fine aside from the color change, they should be safe to eat!