Screws - older houses used STEEL boxes and straping. They may have a touch of rust on the screw.
Amps/switch - the switch is matched to the curcuit on the panal. ie - 15 amp curcuit from the panel gets a 15 amp switch, 20 amp curcuit from the panel gets a 20 amp switch
wire color - switches are power in and power out. color never matttered in a switch because there is no appliance. ie - hot and neutral vs a switched leg
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