diff -y is side-by-side. As far as I know colordiff does per-line coloring, while icdiff seems to have finer granularity. This dude really should have patched colordiff, though. Or just used emacs.
colordiff is just a perl script to colorize diff's output. Patching it to add support for the kind of coloring I want to do here would be a lot of work.
As for using emacs, there are many cases when I want a stand-alone diff tool.