Google Calendar V3 API returns null in colorId [closed]

I have a service account and trying to access www.googleapis.com/auth/calendar events
I’m able to read all the events but colorId is always null.
When I try via APIs Explorer I get all the colors.

Any suggestions?

Thanks.

Edited as per request:
you need a service account with www.googleapis.com/auth/calendar scope applied end read all events. colorId will be null