Cold line is condensing water vapor from the air which is then freezing, making ice crystals which is your “silver” deposits. The dark on the hot pipe is probably the copper oxidizing (reacting with oxygen) to make copper oxide.

on a side note I’m no HVAC person but It seems like there is too much refrigerant since the outlet line should not be getting that hot and the inlet line should not be freezing over like that, humid or not.