I tried to find what you are talking about but there were several possibilities. They were all really pretty though. Whichever one it is that you want, I can see why. Do you know the botanical name of the tree you want? Have you asked on the CA forum?

purpleinopp, if I'm not mistaken, Cassia x nealiae is the name of the rainbow shower tree because it's a hybrid. I haven't asked but I have looked around. There wasn't much, so I'm still doing my research.

See link below.

Here is a link that might be useful: Rainbow Eucalyptus (Eucalyptus deglupta)

The Rainbow Shower Tree is a cross between Cassia fistula and Cassia javanica. There is a Golden Shower Tree and that's Cassia fistula. The Rainbow Eucalyptus is entirely different.

Hi
cassias are quite common is s florida While beautiful they tend to seed like crazy There are some sterile hybrids
Only species I have left is Cassia roxburghii which flowered
for the first time this year . Very disappointing, instead of being bright red was a dull orange so far seeding has kept to a minimum and it does make a very lacy canopy
Guess it will stay lol gary

A lot of Cassia species are declared weeds in many areas. And even if they're not prohibited it's often strongly recommended to not plant them.

Rainbow Shower Tree - Cassia fistula x javanica is sterile, so...