Using a Asus Prime Z370-a mobo connected a CoolerMaster 1-to-3 splitter cable from the RGB header to 3x MasterFan Pro RGB 140mm fans.
LEDs are synched using Asus Aura but NO BLUE. Red and green working perfectly fine.
Tried to calibrate using Asus Aura. Red ok, green ok, when blue is selected no lights at all.
I tried disconnecting 2x fans so that only 1 is connected to the splitter cable. No joy.
Connected 1 fan directly to the RGB header on the motherboard and blue works, so fans are definitely fine.
Replaced the splitter cable, thinking the first one was faulty - blue still doesn't work!