Plugin "Calendar for Jira," it is possible to select custom colors for the calendars based on hex codes.

  1. Click on the color icon when creating or editing a calendar.

  2. At the bottom of the popup, there is a field for entering the color hex code.

  3. Enter the color code.

The color code can be found, for example, in the configurator in the Google search engine at the request of Hex Color.