How Imfuse works? what is the difference between green and magenta?

I used imfused [ C1=imfuse(I1,I2,'falsecolor','ColorChannels',[2 1 2]); ]. The result is an image with gray, magenta and green colors.

Reading matlab documentation, "Gray regions in the composite image show where the two images have the same intensities. Magenta and green regions show where the intensities are different."

Question; What is the difference between gray and magenta here? why matlab colors them differently?

Another question, can someone brefly explains how imfuse works? or any link that I can educate myself?

Thanks a million