Currently the Calendar plasmoid shows that some day is a holiday only when I click the particular date. This is not practical at all - let's consider I am planning a business trip to some other country and I want to check if there are holidays there during the planned trip period - currently to get this information I have to click each and every day of the planned trip, one by one!

Proposed improvement:
1. Extend the 'Holidays' configuration section, for each selected region the user should be able to choose a holiday color
2. The Calendar plasmoid should use these colors to mark the days in the month display.

Notes:

- At least two colors should be available - so one can easily distinguish between holidays in his country of residence from holidays in countries he often travels to.
- Ability to display holidays without marking them in the monthly view (without selecting the color) might also be useful for someone (for example, if he cooperates with people from this country, often talks by phone, etc. - but never visits it)
- It would also be nice if (after clicking on the date) the plasmoid could display not only holiday names, but also region names they are related to.

Reproducible: Always