Generally, gold contacts are used in low current circuits (a few mA) such as inputs to a micro-controller or PIC.
Silver contacts are used for high current (a few amps) such as switching power.
Gold is used because it does not tarnish and works well in "dry" circuits, ie very little current.
Silver is used because it has a very low resistance. It does tarnish, but when switching a load, the current is able to "burn through" the tarnish to give a good contact.
Silver contact switches, when used in low current circuits will soon give problems of bad contact.
Chrome contacts? never heard of it.
JimB