For the first 5 weeks a team is considered in uniform if that a team is clothed in tops (t-shirt, polo, etc) of a similar colour. The tops do not need to be the same but they do need to be close enough in colour and design that the referee can tell players are on the same team.
After week 5 there is an additional requirement for unique numbers on the back of each uniform, numbers can be in taped, drawn, or pinned on but they must be legible to the referee. Teams may be penalised for players not in uniform.
The penalty will be in the form of tries per player not in uniform awarded to the non offending team (up to a maximum of 2 tries), note this must be done before the game starts, teams should not be penalised for missing uniforms at the end of the game.
Whilst using white in combination with another colour in your team uniform is okay, teams should not choose a uniform colour that is predominately white, as this is the designated referee colour.