Cross references: Eukaryotes Prokaryotes Prokaryote Colonies
Slime Molds Parazoa
I was surprised. Unlike the voluminous literature on prokaryote colonies, there is almost nothing available on eukaryote colonies.
In particular, there is nothing on how the constitutent cells communicate with one another.
I think this may be because some of the prokaryotes are parasitic pathogens which cause disease and have been studied intensively in search of treatments for the diseases they cause. As far as I can tell, the eukaryotes are not pathogenic, and, as a consequence, they've been pretty much ignored.
"The Volvocaceae are a family of unicellular or colonial biflagellates"
All of these links are active, and if you click on them, you'll see that many of the colonial forms show close coordination among the individual members. However, I could find nothing on how this coordination occurs. Chlamydomonas"
"Chlamydomonas is a genus of green alga. They are unicellular flagellates. "
"The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals." "The choanoflagellates feed on bacteria"
"A number of species such as those in the genus Proterospongia form simple colonies,planktonic clumps that resemble a miniature cluster of grapes in which each cell in the colony is flagellated or clusters of cells on a single stalk. 
But, again, there is no information on how the individual cells communicate with one another.