Not sure if this is a bug, but montage does not seem to support transparency in images.
convert logo: -resize 50% -transparent white logo2t.png
montage logo2t.png logo2t.png logo2t.png logo2t.png -channel rgba -alpha on -geometry +10+10 -tile 2x2 logo2t_montage.png
Resulting image has no transparency. Is this a bug? Or am I misunderstanding something about montage?
This works, so I guess I just needed to use -background none
montage logo2t.png logo2t.png logo2t.png logo2t.png -background none -geometry +10+10 -tile 2x2 logo2t_montage.png
But it would be nice to have transparent images with other color fill between the images.