most of mine do not grow into each other they tend to move or go another way when getting close to another one. they will grow on the back side of each other , i am sure if they are the same type they might blend a little based on the "tow differnt monti growing together thread" on another forum. overall when two more more are growning next to each other it makes a great view in the tank or tanks. the only down fall i have seen is one part of the caps can shade another cap below is and the lower one will bleach or dye out due to the lack of light which is normal and doesn effect the cap in any way or growth.
I have two places where I have orange touching green. I glued one of each on the back wall and have noticed that the green is now showing orange polyps. The edges would bleach but as previously stated, once they got to know each other, all is well. BTW, the orange grows faster than the green.
when they got to the point of touch they seem to back away from each other and grow on the bottom or back sides of each other but not where there is flesh. this was a months back and they still are avoiding each other with a much large area of what i can call "none contact" i did cut away part of the purple one so the green one could grow over the purple one. as the green one grows slower. when i got the green one it was only 1" x 1/2" in size.
Man there is a kick butt pic out there where someone (I believe a member here) took a bunch of pieces of red and green monti and glued them together like a checkerboard. It grew out and looks awesome!
I remember the one Rev is talking about too - pretty cool; he used four pieces if I remember correctly. Not it obviously, but here is my purple-red and green w/pink edges when they started growing into each other. To the point now where I can't get them in a single picture.