In brief
outline-color sets the outline's colour. When customising keyboard focus, it needs to remain distinguishable from the surrounding background.
Useful to know
outline-color sets the outline's colour. When customising keyboard focus, it needs to remain distinguishable from the surrounding background. [1]
Check the control across every theme and image used. A colour visible on white can disappear over a photograph. Do not remove the only focus indicator merely for a cleaner appearance.
Sources
For further detail and to check the information: