Touch, Visuals category, VoiceOver Utility on Mac
Use the Touch pane of the Visuals category in VoiceOver Utility to customise the transparency of the background that dims the screen around the focus area. This pane is shown only if a trackpad is available.
To open VoiceOver Utility, press Command-F5 to turn VoiceOver on, then press VO-F8.
Note: VO represents the VoiceOver modifier.
Drag the slider towards 0 per cent or 100 per cent to decrease or increase the transparency of the dimmed background around the focus area.
If you increase the transparency, the background colour becomes lighter and you can more easily see the rest of the screen.