To assume is to error...
Our white is also primary and seconday ground color.
Primary positive is red, secondary is black.
Most other positive leads, lights etc are purple, few othes, blue, yellows. So for me first assumption (before testing) Is if its colored its positive.
Where I get into trouble is on couple things that use black for ground, the red & black.
So for me (without testing) if its colored it ususally hot. But I never assume polarity by color.
EDIT:
Umm just reread Redskys post, missed where also said house was white positve? Black was negative?
REALLY?