~/.subversion/config の diff-cmd に指定して Git の [color] ui=auto 風に

autocolordiff.py

#!/usr/bin/env python

import sys, subprocess

class AutoColorDiff:
  diff = 'diff'
  colordiff = 'colordiff'

  def run(self, args,
    stdin = None, stdout = None, stderr = None,
    close_fds = True):

    diff_cmd = self.diff
    if stdout == None:
      stdout = sys.stdout
    if hasattr(stdout, 'isatty') and stdout.isatty():
      diff_cmd = self.colordiff
    args.insert(0, diff_cmd)

    return subprocess.Popen(args,
      stdin = stdin, stdout = stdout, stderr = stderr,
      close_fds = close_fds).wait()

if __name__ == '__main__':
  exit(AutoColorDiff().run(sys.argv[1:]))