[TheFluff]

@devilcoelhodog: I'm not sure that I understand what you're talking about, but maybe one of these options are what you're looking for...:

Originally Posted by Aegisub manual, Options section

audio draw selection background=BOOL
Controls whether the background for the current audio selection is shown in different colors or not. Defaults to true (1).

audio inactive lines display mode=NUM
Controls how Aegisub displays the lines surrounding the currently selected one in audio mode. Valid modes are:
0 - Disabled (only show the current line)
1 - Show the previous and next lines in grey (this is the default behaviour)
2 - Show all unselected lines in grey

audio line boundary start=HEX
audio line boundary end=HEX
The color of respectively the start and end line boundaries in the audio view, as hexadecimal RRGGBB values. Both default to #FF0000.

audio line boundary inactive line=HEX
The color of the lines surrounding the currently selected one in the audio waveform (see the audio inactive lines display mode setting). Defaults to #808080

audio line boundaries thickness=NUM
Thickness in pixels of the boundary lines for the current audio selection. Defaults to 2.

audio selection background modified=HEX
The color of the background of the selected area, when modified but not yet committed, in the audio view, as a hexadecimal RRGGBB value. Defaults to #5C0000.

audio waveform selected=HEX
The color of the selected area of audio waveform, as a hexadecimal RRGGBB value. Defaults to #FFFFFF.

grid inframe background=HEX
The color of a line in the grid that is currently visible in the video display. Defaults to #FFFDEA.

grid selection background=HEX
The background color of a selected line in the grid. Defaults to #CEFFE7.

grid selection foreground=HEX
The foreground (text) color of a selected line in the grid. Defaults to #000000.

Refer to the aegisub manual, options section, for more details on how to set these options.