I used a deep dusty pink ground base colour (see pic below) which allowed me to see the white petals of the magnolia.
Broad strokes were used with not too much fussy detail. The tonal differences were very small, I did light the flowers from the side to create more shadows and interest.
I decided to paint over the top of the dusty pink ground in a similar but lighter colour graduating it as I went up the board also leaving gaps so the base colour shows through and links it together.