RGBW header
RGBW header
It’s fine to use a 4-pin connector into a 3-pin LED header. The RGBW header you described is common for fans, and the mismatch in pin count doesn’t prevent proper connection. The 12V RGBW header is designed for fans, so it’s perfectly acceptable.
The label you're referring to appears to be an addressable RGB header, not a fan header. On the markings you can clearly see R on one pin, g on another, and b on a third. The first pin is for 12V, and the last pin is designated for white.
You're asking about compatibility issues with fan cables. It seems you're wondering if linking a 4-pin fan cable to a 3-pin RGB header won't work, but there might be exceptions depending on the setup. It also mentions that swapping the pin configuration could potentially solve the problem.