Hi,

You can use the following code in your custom CSS to change the active dot color:

.pitech-service-carousel .sp-slider-custom-dot-indecators .sp-text-thumbnail-list .sp-dot-indicator-wrap .dot-indicator.active {
    background-color: red;
}

To change the rest of dots color with lower transperancy:

.pitech-service-carousel .sp-slider-custom-dot-indecators .sp-text-thumbnail-list .sp-dot-indicator-wrap {
    background-color: rgb(48 228 11 / 40%);
}

Note: Path towards custom CSS(Joomla 3): Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.

Best Regards