Simply set it in the main styles.css, changing the values you need. Use only what you need, I set here all the possible values:
.mat-mdc-slide-toggle {
--mdc-switch-selected-handle-color: #ffbb1c;
--mdc-switch-selected-pressed-handle-color: #ffbb1c;
--mdc-switch-selected-pressed-state-layer-color: #ffbb1c;
--mdc-switch-selected-hover-state-layer-color: #ffbb1c;
--mdc-switch-selected-hover-handle-color: #ffbb1c;
--mdc-switch-selected-focus-state-layer-color: #ffbb1c;
--mdc-switch-selected-focus-handle-color: #ffbb1c;
--mdc-switch-selected-track-color: #e0e0e0;
--mdc-switch-selected-pressed-track-color: #e0e0e0;
--mdc-switch-selected-hover-track-color: #e0e0e0;
--mdc-switch-selected-focus-track-color: #e0e0e0;
}
My favorite values are only 2: the track and focus-track colors, to only change the background color of the slider:
.mat-mdc-slide-toggle {
--mdc-switch-selected-track-color: orange;
--mdc-switch-selected-focus-track-color: orange;
}