Adding Simple Custom Field to Django -- How to Write South Introspection Rules

I am trying to add a custom field to my Django project that uses South. Because of this, I am trying (for the first time) to write introspection rules for South. I believe my case is the simplest possible as I am simply extending a CharField. Specifically:

class ColorField(models.CharField):
    def __init__(self, *args, **kwargs):
        kwargs['max_length'] = 10
        super(ColorField, self).__init__(*args, **kwargs)

    def formfield(self, **kwargs):
        kwargs['widget'] = ColorPickerWidget
        return super(ColorField, self).formfield(**kwargs)

This is from a Django snippet called jQuery color picker model field for those interested.

Since I am not adding any new attributes, I believe I only have to add these lines of code:

from south.modelsinspector import add_introspection_rules
add_introspection_rules([], ["^myproject\.myapp\.models\.ColorField"])

It is probably obvious, but where should they go? Also, is my assumption that this is all I have to do correct?

I have reviewed several questions posted here, but most deal with much more complex introspections.

Per http://south.readthedocs.org/en/latest/customfields.html#where-to-put-the-code, I have tried puttin the code at the top of my models.py file where the custom field is defined. But this has not worked.