I'm replacing my theromosta and don't know which wire is what, Have 4 wires red, blue, green, white/Yellow is there a commont color for heat, air, fan etc

The normal colors are:
Red is the 24 volt hot wire from the transformer
The green is the power back to the blower motor relay.
The white is the power back to the gas valve.
The yellow is the power back to the condensing unit.

You said you have four wires but you name five.

It looks like you meant one wire to be called a yellow with white. In that case I would think it was the gas valve and the blue was the AC unit.

Give me more details and I will try again to help.