I had that happen, and I'm sorry to say, could never get the micro back to the original color inside.

It might be time for a new microwave. I had one that worked great for years and then slowly it was not doing things so well. One day it started making a noise and it stunk.

I replaced it with a new one and I could immediatly see how the old one was probably failing for some time. I've been very happy with the new one (even better than the last one).

It will never go away. You can't clean off a burn,the material is actually damaged. It is not a "stain". I would replace it.

I am no help at all!! I haven't burned anything in mine, but I do have a SS interior and it is impossible to clean!! I have done all of the steam techniques...even the one listed above and nothing works! I called the manufacturer and they sent me a product that PLAINLY states "Do not use on SS microw interiors"....huh?????
Lizzie, thanks for letting me gripe on your thread...I apologize for interfering...hanging head in shame.....