It’s not a RGB color change because it’s a different attribute. The two attributes are changed independently, color temperature and RGB color.
It’s up to the author of each smart app/routine to provide the ability to set the two attributes, and many authors were only used to working with Philip Hues, which don’t have temperature controls.
I believe rule machine has either added temperature controls or is going to shortly, so you could take a look at that. It would install as custom code but offers many more control choices than smart lighting does.
This first topic covers how you add custom code.
If that then sounds like something you would be comfortable doing, then
The following topic has the code for rule machine: