dyeing linen

[Lepidina]

Why is the assumption made, as you have in this case, that persons pictured doing menial labor are slaves? Why would Roman artists constantly picture slaves and not freemen? Why would they show slaves richly dressed and not as they would have been-in rags? Perhaps this mosaic (Villa Armerina) seeks to depict slaves, but is this the rule to be followed in all mosaics? Are all persons depicted doing menial labor assumed to be slaves, no matter what other features are shown?

Why are you assuming that all slaves wore rags? Some slaves wore rags. Some slaves wore really nice clothes. Some freeman/citizens wore rags. Some wore really nice clothes. The argument that anyone doing menial labor may or may not be a slave is a decent one. I assume that in some cases, there are clues in how people are drawn or from the context of the picture that denotes status.

And yes, I think that there is a general argument made in this thread that Roman soldiers must have been clothed in white and not in colors. For example, in this thread:

-White shows status because it requires cleaning.

There's also a huge tradition of white in military clothing as well, probably because it's easier to bleach a whole load of white trousers than to separate out colors in laundry. Military clothing does not necessarily follow the same fashion rules as civilian clothing.