Add Option for Background Color and Font Colors for each calendar

[skilly00]

Small bit of code to add background color for each calendar if desired. Also readme was updated to explain and add function for legend which was missing.

[whittssg]

@skilly00 Should an option be added for font color at the same time if this pull is allowing for background color change? I know card mod would work but might be easier adding another option. If the user adds a really light background the default font color wont show well.

[skilly00]

@skilly00 Should an option be added for font color at the same time if this pull is allowing for background color change? I know card mod would work but might be easier adding another option. If the user adds a really light background the default font color wont show well.

I added that per your request I have tested it with Firefox and Safari and all changes made work.

[FamousWolf]

I'd rather keep the number of options, especially for styling, limited where possible. You can already style events for each calendar differently using card_mod, as each event has a data-entity attribute with the calendar entity. For example:

card_mod:
  style: |
    .container .day .events .event[data-entity="calendar.my_calendar"] .title {
      color: #ff0000;
    }

This will change the title color for events from entity calendar.my_calendar to red.