Why are some on/off square parameter toggles half filled with a diagonal triangle?

Hello everyone,

I just made a Title in Motion then published it and some individual parameters to FCPX. In FCPX, I noticed that some of the parameters on/off activation squares are not a solid square, rather, they are filled with a diagonal triangle. What is the difference between being completely filled and diagonally half-filled?

I tried to find this via search both on the forum and via Google to no avail!

Any help/insight appreciated.

~Shea A.J. Comfort