How to change color for mat-divider?

To change the color mat-divider simply change the border-top-color property of .mat-divider class.

.mat-divider {
  border-top-color: red;
}

https://www.angularjswiki.com/angular/angular-material-divider-mat-divider-example/#mat-divider-color

Yes, you can.

You need to overrule .mat-divider class styling in your own written CSS and change the border-top-color property.

.mat-divider {
    border-top-color: rgba(0, 0, 0, 0.12);
}

is the default styling by Angular Material.

.mat-divider {
    border-top-color: red;
}

This should be enough to change it (if your CSS gets rendered later than Material's). Otherwise adding increased specificity to your CSS class will help (f.e..mat-divider.mat-divider).

StackBlitz example for this case.