Hi
I have now tested the Zener diodes ZD301 Z311 ZD321 in circuit with my multimeder, they all test the same value.
I have also tested the color drive transisters Q302 Q312 Q322 in circuit with my multimeder, they all test the same value.
Also the Resistors R306 R316 R326 they also test OK in circuit.
But I am thinking to swap one transistor first, then test to see if i am missing another color, if not swap a zener diode, or just replace the one at the blue color