If not, how does the phone decide which tiles to color in "theme color"?
Thanks in advance
In general: No, there is not.
All of the standard Phone functions have colors recording to the chosen theme color, except the Music and the Games tiles. Most likely just a design choice (I don't like) as they are animated in the two larger sizes.
For every other app, the developers can decide. If for example Google wants its logo as a tile, they can do that.
Now I wrote that you can't change it in general, but there are apps that let you exchange some of the basic functions to some extend with other pictures, for example Wiztiles. I don't use these, maybe someone else can write something more about them.