Managing meetings and events using Outlook on the web for business
I don't think the shared Microsoft Bookings calendar currently supports assigning a different color to each service type.
Microsoft does document color categories for personal booking meeting types, but the shared Bookings service settings don't include a color/category option.
So the Outlook conditional formatting rules would apply to the Outlook calendar view, not change the colors in the Bookings calendar itself.
Using different staff members as a workaround can also affect availability and allow the same time slot to be booked, so I wouldn't use that just for coloring.
If anyone has found a newer Bookings feature that adds service-based colors to the shared calendar, I'd be interested to know as well.