Based on feedback from comments, updated my answer by removing ‘::ng-deep’, but please read comment by @colin-fox, and understand how this will behave in global styling and at component level, many thanks!
For Angular Material 7, works for outline color and inside filled in color
.mat-checkbox-checked.mat-accent .mat-checkbox-ripple .mat-ripple-element {
opacity: 0.03 !important;
background-color: #005691!important;
}
.mat-checkbox-checked.mat-accent .mat-checkbox-background,.mat-checkbox-indeterminate.mat-accent .mat-checkbox-background {
background-color: #005691;
}