Confusion - of all sorts - can sometimes arise when an aircraft is being operated by one company but in the livery of another. At busy airports, by saying follow the company 737 or whatever, the controller is reducing the risk of the wrong aircraft being identified by the following pilot and, sometimes, reducing the RTF necessary. Using this technique when the company aircraft doesn't look like a company aircraft is poor practice....and confusing to others who do not have the same situational picture that the pilot and controller involved in the exchange may have.