2 or 3 LED colors on a single digital pin

[TomGeorge]

@LarryD

But D1 is reversed biased so the Q1 gate stays at +5V.

Hence Q1 is turned OFF.
Gate is at Source potential, P_CH MOSFET.
Without diodes, Q4 and Q1 gates connected with R1 and R2 as potential dividers, so both gates at 2.5V and -2.5V with respect to their sources.
So need the diodes.

Tom....