It's one of the oldest sayings in aviation circles: "If it's red or dusty, don't touch it." It seems obvious enough not to touch buttons or switches when you don't know what they actually do, so how did this axiom become so common? Older planes with less intelligent avionics apparently had to be safeguarded against human error.
Still, accidents happen... because some people just have to touch the red button.
Planes from the Vietnam Era such as the F4 Phantom and others, even those entering service much later, like the AH-64 Apache helicopter featured red buttons and switches with red, protective coverings to prevent maintainers and pilots from accidentally pushing or switching them. The reason is they perform critical functions that should only be used when the situation calls for it.
For example, there's no off-label reason to jettison your fuel tanks on the tarmac, as it turns out. This is the kind of prevention the color red is ideal for. Dusty switches are just controls that might be less obvious but are rarely if ever actually used.
You probably shouldn't jettison anything while on the ground.
In Air Force flight school, new pilots are instructed, "don't f*ck with the switches with red guards." These control irreversible and potentially deadly functions in the cockpit, things that could really ruin any pilot's day if accidentally toggled without reason. Often they are to be used in emergency situations only. This isn't only for the pilots, but also for maintainers and anyone else who might be sitting in the cockpit while untrained or unsure of what they're doing.
The military tries to make everything perfectly idiot proof, but the combination of complex controls with a high operations tempo can make anyone tense enough to make mistakes, cut corners, or just accidentally pour jet fuel everywhere you don't want it to go. This phrase may have originated in the Vietnam War to keep new, potentially drafted troops aware of what they were doing and where they were doing it, to keep going through their lists and stations, even when the "Rapid Roger" tempo was very high.