I pull the centers out of old black watercolor markers and put them in the glue
bottles. Let them sit overnight and the next day you have great black glue. It
looks very dark green when it is wet but when it dries it is black and shiney.
I used to mix tempera paint with my glue but I found it developed (rather
quickly) a bad smell. The marker process has no odor and lasts for a long time
and works better than the colored glue you buy. I have tried it with other
colors and it works with them too. Carol