On a simple circuit containing a tri color LED (Part Number: 5988740302F) when power is applied the LED only lights up Green but should be Blue when 5VDC is applied. To explain the troubleshooting, 4.4V was measured across the +5V node and ground. On another circuit (the good circuit) the LED is lighting correctly (Blue) and the measured voltage is 4.6V.
More troubleshooting: On both circuits When the cathode of the Yellow LED is shorted to ground, the LED lights up Yellow.
Is it possible that something in the circuit is driving the voltage down? There are other parts of the circuit that driven by +5V.
Forward voltage (from datasheet): 3.2V Blue, 3.2V Green, 2.2V Yellow