I got a brand new mossberg 500 for christmas, I took it out shooting, I must have laid the case in a puddle or somethin and didnt know it was wet.  When I took the gun out, there was a small spec of rust on the very end of a barrell, I guess I was a little to harsh on it when I removed it, because now the rust is gone, but it looks like I took a little bit of the bluing off, theres a tiny spot on it about the size of a cookie crumb that is almost chrome in color now.  Im wondering, if I got a bottle of cold blue, and used just a very very small amount, if I would be able to fix that, or would it end up just looking worse and I should leave it alone?  

no one knows if I should do this?

That should work.
You'll need to really degrease the area well, and apply over as small an area as possible.
Often, cold blues will discolor the original blue around the area being touched up.

For that reason apply only where you have to.

Warm the metal first.  Warm.....NOT HOT, just warm.
After bluing, rinse with hot water, then apply a good lube to prevent rust.

I've been using the Brownells oxpho-blue creme to touch up a Remington 1100, and I've been pleased with how it blends in. The nice thing about the creme is that it's not subject to expensive hazmat charges, and you can use a q-tip to apply it just where you need it and not have to worry about it running all over the gun. It should look good as new if you use it on your gun, and unless your gun is heavily soaked in oil, you don't even have to degrease.

Thanks for the helpful info guys.