Install colordiff and configure Subversion's diff-cmd.
On Mac OS X, you can install colordiff using MacPorts.
$ sudo port install colordiff
On Debian or Ubuntu, you can install colordiff using apt.
$ sudo apt-get install colordiff
On other systems, you can download source tarball from http://www.colordiff.org/ and install colordiff.
[helpers] diff-cmd = colordiff
$ svn diff | less -R