it may be burnt looking. the best thing to do (unless you have a multimeter, which in your case is highly unlikely considering the type of thread you have made) is remove them one at a time and look to see which one is bad. once you find the bad one, replace it with a good one of the same amperage. you can go to any parts store and ask them for the same exact replacement fuse. you can take it out once you find it as it is serving no purpose in your vehicle, so don't worry about that.

i suggest before you do replace the fuse, go get some electrical tape (the good kind) and tape up those connections behind you radio really well so that they never touch again. then replace the fuse.