`color` is not a standard `logging.Formatter` constructor argument - with this change you'd only be able to use subclasses of `tornado.log.LogFormatter` (or other formatters that implement a `color` argument), instead of any `logging.Formatter`.  If we support configuring formatters by specifying a class on the command line, that suggests that formatters should not take constructor arguments and we should in fact have separate classes for colored and non-colored output (or more generally, different formatters for file and stderr output).  This is getting complicated for command-line configuration.  I think that if you need to customize your log output you may just need to forego Tornado's automatic log configuration and just configure logging yourself (either in code or using the logging.config module).