I've decapped hundreds of live ones normally, not one has popped. Fear of primers is vastly over rated; primers are quite small, they are not sticks of dynamite. If one did go off while decapping normally it will hardly matter because the whole thing is well enclosed by the die and a popped primer sure won't blow a steel decap assembly out of the top of a die! What COULD be a mistake would be to allow a pile of live ones to collect in the catcher because it MIGHT be that if one does go the cup could/maybe/possibly go down with enough force to set the collection off - but that's quite unlikely too.
If the brass is simply discolored, load and shoot it. Shiney cases aren't more accurate nor are they any safer to use than tarnished stuff.