The Toga: badge of Roman citizenship.

photo Toga Party Costumes - Buzzle

Toga was THE national garment of Roman citizens:  a woollen cloak with curved hem.
For men it was a symbol of their free-born status. 
Augustus revived the toga and invited Romans to wear it in the Forum and when attending races at the Circus.

Late antique writer Macrobius describes in his 'Satires' (3.13.4) the complexity of being a dandy for Hortensius: [...] to go out well dressed he checked his appearance in the mirror, and so draped the toga on his body that a graceful knot gathered the folds, arranging them not randomly but with care [...] He thought it a crime that folds should be moved from their place on his shoulder [...]

It was a statement which underlined the Roman citizenship.
Initially it was made of undyed white thick coarse woollen cloth.
A dark toga: brown or black (toga sordida) was used by poor citizens, accused people or for mourning.
Victorius generals in their processions wore the special toga picta (purple wool and gold thread).  Also worn by kings initially, emperors later, equites and priests.
The toga praetexta was for high rank people:  it had a purple stripe (clavus).
Young Roman boys, once they turned 16,  were allowed to wear the toga virilis or liberior (since it meant they were free from parental control.)  It was also named toga pura because it was white.
For the Romans dress was, like nowadays, an expression of social rank, gender and age.