What colour has been your favourite of all the cars you've owned in the past?
That's a good start.

Oh, and eliminate those colours which you would not want based on past experience.
For me that would be silver and any variation of silver down to gunmetal grey. Dark green, Dark blue, Dark red, Fridge white.
Then see what's left.
Google "what colour" Morgan images and see if you like what comes up.

DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4