Hey, if you could resubmit with further information, that would be great. What phone do you have where you are trying to change calendar colours, what calendar app you're using.
For example if it's Google Calendar I find it easier to change the calendar colour online. However, if it is your phone, raise a new appointment and top right in the calendar you have selected there is an artist's palette, click on that to change the colour. You can also change the colour under 'calendars to display'.
You could also register on the site to get help also.