Hi Arthur.

You forgot to share example URL or screenshot link (I have to be sure that we both thining about the same).

But let's say that we talk about "day" color

In that case you have to use Custom CSS to override them, example with new colors(!)

.eventum-schedules.layout-addon .eventum-schedule:nth-child(1) .scedule-date-day, 
.eventum-schedules.layout-classic .eventum-schedule:nth-child(1) .scedule-date-day 
{color: green; }

.eventum-schedules.layout-addon .eventum-schedule:nth-child(2) .scedule-date-day, 
.eventum-schedules.layout-classic .eventum-schedule:nth-child(2) .scedule-date-day 
    {color: yellow;}

.eventum-schedules.layout-addon .eventum-schedule:nth-child(3) .scedule-date-day, 
.eventum-schedules.layout-classic .eventum-schedule:nth-child(3) .scedule-date-day 
    {color: blue; }

.eventum-schedules.layout-addon .eventum-schedule:nth-child(4) .scedule-date-day, 
.eventum-schedules.layout-classic .eventum-schedule:nth-child(4) .scedule-date-day 
    {color: pink; }

.eventum-schedules.layout-addon .eventum-schedule:nth-child(5) .scedule-date-day, 
.eventum-schedules.layout-classic .eventum-schedule:nth-child(5) .scedule-date-day 
    {color: brown; }

.eventum-schedules.layout-addon .eventum-schedule:nth-child(6) .scedule-date-day, 
.eventum-schedules.layout-classic .eventum-schedule:nth-child(6) .scedule-date-day 
    {color: red; }