HEllo Martha,
I understand why color coding is useful. The location of that option has changed in newer Outlook versions.
It's now under Categories. Instead of going to File, open your calendar, right-click an event, and select Categorize to assign colors. If you don't see Categorize, your account type might not support it.
Are you using the Outlook desktop app or the web version, and what type of account do you have?
Outlook doesn't let you completely switch back to an older layout, but I can show you how to customize the ribbon to make Categorize easier to access. Would you like me to guide you through adding it back?