I am not sure I follow, x-newa does fill the colour of entire cell in the EPG with the genre colour. However first-runs show hightlighted text, perhaps you haven't set the genre colours yet?
When I view the guide in NEXTPVR, the cells are filled with the different colors I have selected using the genre button, but all the type on the grid is displayed in white. That's the way I thought it should look.
When I view the guide in X-NEWA, all of the cells on the grid are displayed in grey, with only the type being shown in the colors I have selected.
It's sort of the reverse of what I thought it should be.
I'm sure it's something that I don't have set up properly.