Jon added Net Tools in the development version of pcbnew. Quotes from the news thread:
Thanks to Jon, we can now hide ratsnest lines for a net. Select a board item belonging to a net (most often this would be GND or some other ubiquitous net which makes it difficult to discern other nets). Open the context menu and you’ll see Net Tools and can hide/show the selected net.
There’s also some backend support for coloring nets, but there’s no GUI yet.
Updates, comments and questions are welcome here.