It is configurable now for most known states.
Through themes
Why not simply add the option to change the colour you want. Is it that difficult? Whats the reason behind this?
Yes it’s difficult or else somebody would have added it.
it’s also that difficult to integrate the option to choose the colour in the calender for different calenders? I have totally no idea about programming, but im just wondering how hard it must be to make this possible. Maybe you can help me understanding this. thx!
An entire theming backend and front would need to be developed to make this point and click. It’ll be semi difficult, time consuming, and require constant maintenance. It would be best if you just took the time to learn the theming provided in the frontend integration docs. Otherwise you’ll be waiting a long time for a feature like this to be added.