I was very pleased with this magnolia when I bought it last year. The flowers were supposed to be yellow with red at the base of the flower, indeed that exactly what the single flower last year was like. See https://365project.org/susiemc/album-1-year-6/2018-05-04 This year the flowers are very definitely white with a red base. I don't understand what's happened.
A lovely flower - but you must be somewhat disappointed not to have the more unusual flower colour - perhaps it is to do with the acidity or lack of in your soil ! - just surmising !!
It's lovely, but has changed from last year - I wonder if Beryl has a clue there - could be worth checking out to see if you can influence the flower somehow
