I'm not exactly sue about what you mean by audio grid. If you mean the horizontal line that represents the volume level (if it's under the top of the audio event it means that you've lowered the volume for that audio event), then no, I'm not aware that it can be removed. An alternative is to go to the bottom of the track header and, with your mouse, drag the height of the track down to enlarge it - or use the track header size selection option to expand the size of the track to a larger size including maximum.
As stated, you change the colors in the display menu. The blue 'Volume' line can be hidden (keyboard shortcut: V) and/or the color can be changed. (also in display). The white 'Gain' line can be dragged to the top where it disappears (volume can be adjusted by other means).