Quark has an option wich enables to make the grass greener, it changes too the colour of the tall grasses and trees folliages, but the Biomes O Plenty grasses and folliages keep the original Vanilla color.

It is not really possible to add support for this in BoP itself. It is possible to do in Quark though - might look into doing a PR at some point for this.
It is also possible to add whatever blocks you want to be affected by this in Quarks config in case you didn't know :)

Quark already added a support for it since some updates, now it's possible to list the blocks which can be greener. Sorry if I didn't close this issue before, I thought I had already did, anyway I close it now.

But in Omnious Woods, the grass is vanilla one, so there is no way to disable this feature, except disable Grass Greener completely.