Disassembled A/C low pressure switch parts labeled, plus yellow…

The guts of an A/C low-pressure (clutch-cycling) switch

The color distinction refers to the ACCUMULATOR/drier's threads; not the refrigerant itself. The plastic threads in the switch base are sized for each type of accumulator. If using an R12 accumulator in a system converted to R134a, use the R12 switch to match the accumulator, but adjust its pressure point to ~22psi using the procedure in this TSB:

Owner caption September 2014 · Photo 5219 of 6546