Are the relief solenoid valves all the same (compared to other relied solenoid valves) and are the switching solenoid valves all the same (compared to other switching solenoid valves)? If so then why do every solenoid have a different colour code?

I broke the 6 port solenoid valve. Can I replace this with another solenoid valve from an S4 TII?

 

Yes! (been there- done that)
They are all basic 12v normally closed air bleeds.