Adolfo,
Nothing is impossible with plumeria! They will keep you guessing because you never know what they will do next. Yes, I have heard of this happening. Generally it is the seedlings that can change for the first 3 bloom cycles, but I have heard of cuttings doing the same. Weather plays a part also. In more humid environments the colors will be more beautiful and vivid. It's more common for flower size to get bigger with age and scent to become stronger, but as I said, not impossible to change colors. If you happen to have a before and after photo, we would love to see it.

As far as roots intertwining and mixing, I'm not sure if that's possible as the genetic code is already stored in the plants tissue, but it's an interesting thought.

I have several plumeria planted very close together and so far each has it's own flower.

Congrats on your special tree,
Tony

I have experienced this with mine over the years here in Michigan. The warmer the summer and the more sun seems to do the trick. My oldest plant (9 years) bloomed yellow, until two years ago, when it changed to a rainbow colour. I only plant cuttings. This tree is now a little over 6 feet and in a container that I put out on the deck in the summer.

I made the same experience with my Thai cutting which I bought as 'dark pink'. The first flowers in spring inside the house were a creamy white with pink bands on the back side of the petals. Now on my terrace in full sun this plumie shows the original colour: beautiful pink with veines in dark pink. I hope this colour will change no more!