I have grown a cutting from a plant that was a deep red. In my garden it
is a deep pink.

a similar thing happened to me. The lady next door gave me a cutting from
her beautiful pink frangipani.
It took quite a while to strike, but is now about five foot tall - and pure
white with the typical yellow throat!

Sorry can't shed light on why, though I have a red frangipani, and gave a
cutting to my mother, who lives about 12 kms away, and hers has always been
a light pinkish one! Hers is in more shade than mine, and gets a bit more
love and attention - perhaps that is the difference.