Force RGB in KONA 3

According to the apple color user manual,

When Force RGB function is on, the RGB data in COLOR will send to the video interface (KONA 2 or 3) directly, and let the interface to do the RGB to YUV conversion to monitor SDI out. So it consume less CPU.

When Force RGB function is off, the RGB to YUV conversion will be processed by COLOR, so it consume more CPU.

But something happens to my situation......I have both KONA 2 and KONA 3 in two separate MAC. In KONA2 system, the Force RGB function work nicely, image looks a bit contrasted in my JVC monitor when the function is ON.
But nothing happened in my KONA3 system...!! the function affects nothing, the image on my JVC monitor remain the SAME...

What actually does that means?