Thanks to Howard Katz, who emailed me to say: Many Mavericks and Yosemite users have been disappointed that they seem unable to make the Dock transparent, or otherwise customise its appearance. cDock is a little free app, which not only allows you to make the Dock transparent, but also allows for more extensive customisation for those who wish.
A Thank you for passing on this useful information. cDock does indeed appear to work very nicely under Mavericks, Yosemite, and beta releases of El Capitan (10.11), offering a wide choice of different effects for those so interested. Many such customisations install extensions and do other things which can cause side-effects: cDock works by modifying the Dock’s preference settings, then restarting the Dock app. It should therefore remain compatible and trouble-free.
Although both TinkerTool and MacPilot offer various controls for the Dock, none covers the same type of appearance settings that cDock does.
Updated from the original, which was first published in MacUser volume 30 issue 9, 2014.