What is this?
Eric Newel (https://www.linkedin.com/in/ecnewell/) at Soneridge Software (https://stoneridgesoftware.com/) presents a good solution for creating Office 365/SharePoint Online calendars with color-coded categories (https://stoneridgesoftware.com/creating-a-color-coded-calendar-in-sharepoint-online/).
The only drawback to Eric's solution is these color-coded calendars go back to their default colors when viewed individually. This is one more situation where the Script Editor web part, the Web Inspector, and a little CSS can fix some of SharePoint's UX misses. Above are snippets of CSS for each of the colors in the default O365/SPO theme.
How do I use this?
Follow Eric's tutorial and use the default Calendar view as your "Overlay" view. It's URL will end in something like this:
However, say you have a calendar overlay called Keynote Address. It's URL will end with this:
Wow, thanks! That's helpful! How can I get in touch with you?
You're welcome. Glad to help. I hang my hat here: http://wheatdesign.com