Custom Resolution Utility (CRU)

[BLUuuE]

Hi,
I overclocked my G2460PQU to 160Hz fairly easily, but I noticed that the colours, particularly the greys (looks kinda green), don't look as good. It turns out that running my monitor at 160Hz locks the Color Depth to 6 bpc. At 144Hz, I get 8 bpc, and the greys look much better.

Is this a consequence of running 160Hz?
Is there a way to get 8 bpc on 160Hz?

Thanks