I only have tech. info on the 1977 300D W123 climate control and can't help with color codes. The floor outlet vacuum actuator is found by removing the lower left instrument panel trim cover on my car.
I had to do a very serious diagnostic once to fix my climate control and found the best way to check it was by doing each individual component with my Mity Vac tool (solenoids, actuators, one-way valves, vacuum lines, connectors, etc.). I replaced one vacuum actuator and a couple of one-way vacuum valves (located inline with the vacuum lines). Then I found a short (2") piece of vacuum line that had a leak and then found a plastic "Y" connector that leaked (fixed with a bit of epoxy).
Also I have had broken parts on the vacuum actuator. The plastic piston/rod (connected to the diaphram) that extends out of the vacuum actuator for the center defrost vent has a flat metal rod connected to it with a small rivot that inturn was connected to the control flap for the defrost. The plastic piston/rod was broken where the metal rod connects with the rivot and I fixed it with a bit of epoxy.
So, you need to look for both vacuum leaks and broken parts.
Good Luck!
!
Tom