Gold is the standard short spring that works for all combinations plus lower velocity.
The red spring is referred to as the middle spring. It is longer than the gold spring and is stiffer at the same amount of compression compared to the gold spring which makes the bolt softer on paint. Most of the time it can be used as is for good level 10 performance when operating at about 280fps.
The silver spring is both longer and stiffer and can typically only be used if it is clipped on one end to allow it to be used within a usable velocity range.
Except for the Automag in front, its usually the man behind the equipment that counts.