Dear Mariette Payne (ZA)
Thanks for choosing Microsoft Community.
Based on your description, I know the scenario you met.
If you want to see the color for the calendar you delegate, the mailbox owner needs to assign you at least “Can view all details” permissionsto you (Microsoft 365 Exchange Online) or “Reviewer” permissions (Exchange on-premises).
These permissions include the “Full Details” read permission which is required for displaying Color Categories.
Permissions for Microsoft 365 Exchange Online.

So please be kindly to check with calendar owner whether he gave you thr right permission. If not, please be kindly to give you permission again and check the result.
If there is any update, please feel free to let me know. Your understanding and co-operation are highly appreciated.
Thanks for your precious time. Have a nice day.
Sincerely
Katherine