To my knowledge... They're the same morph but sugar is the line from Europe. Sugars tend to be higher white and not have as many oranges or ringers from what i've seen, just an observation though. It's like Fire and Sulfur.
Think Lesser / Butter - different 'lines' of the same mutation. There are other polygenic differences that will probably wash out over time as people breed for the mutation instead of the overall quality of 'packaged' traits.