Colors

Depending on template / element – color settings can be different. If color settings are available you can find them under Theme Settings -> Section you need to adjust, so if you want to adjust Off -canvas, you would go to Theme Settings -> Off-canvas -> Color
If there are some colors you cannot change it probably means we do not allow, why (?), usually what may seem like a limitation is for the comfort of the user and most likely results from a reason.

If you really need to make some custom changes, I would suggest using Child Theme. Make sure you buck up before you modify.