I suspect that inbreeding through multiple generations is more likely to produce leucistic individuals than crossing with guppies. The super red bristlenose are another example of the same thing, and they certainly weren't outcrossed with a different species. They're essentially calico's that are mostly or completely lacking the darker pigment, resulting in a red fish with dark eyes. If the endler's had the same pigmentation pattern as BN the results would be red endler's.
