Hi Guys,
I think she would have had the blue ensign and not the white. As a hospital ship, she was run by the MOD but she was never classified as HMS, so she would not and could not fly the white ensign.
However as a Hospital ship she would have been part of the "Hospital Group" and this would have given her the Blue ensign. There are more reasons for her using the Blue ensign ie. RNVR Master aboard, RNVR Officers aboard etc. (Check my post-
Britannic - BRITANNIC FROM THE HILLS).
As to the Red ensign, that would have gone as soon as the MOD took her over as a Hospital Ship.
Hope this helps
Best wishes and Regards
Dennis