Jonathan, could you please say more about Coptic vestment colours as I had no idea about this except for during Passion Week.
I'm honestly not sure of the exact rules since it's so disused, but...
Gold is worn on the feasts of our Lord. My priest also wears gold on all Sundays, (and so do I) since each Sunday is a 'little Easter'.
Red is warn during annual time. (Red may also be worn instead of Gold on Sundays of Great Lent, not sure, I stick to gold since my priest does, but on weekdays he wears red so I do. My priest even wears gold on Saturdays, which are non-fasting days like Sundays, but I've never asked him about that...).
So as you see I'm not sure of the exact rule between gold and red, but I know that there is one, I just don't know the details
Blue is worn on Great Friday (note: it is not worn on Holy Thursday), and at funerals.
White or silver (really hard to see the embroidery against the white tonia, but I've seen it done) during the Holy 50. Again, I'm not sure if the gold on Sundays rule superceeds this, in which case it would only apply to weekdays.
I've heard that green should be warn on Palm Sunday, but I don't believe that. A source I trust more has said that green is worn during the month of Koiahk (or alternatly for all of advent). Again, not sure if gold on sundays superceeds this, making it only applicable to weekdays.
In all cased the tonia is white, and these colours apply to the embroidery on the tonia, and to the stole or badrashain.
I personally only have a gold tonia, a red tonia, and a red tonia, each with a stole/badrashain to match... Don't have the other two.
Other random bits: a chanter should wear only a tonia, no stole/badrashain. A reader wears a tonia and a badrashain with both ends at front and crossed at the back. A subdeacon and a deacon wear the stole over one shoulder, and are distinguished by which shoulder (can never remember which is which). Contrast this to the current practice of randomly choosing which one looks pretty...
Also, a 'deacon's' tonia (by which I mean chanters and readers as well of course) should have a cross on the front and should be blank on the back (mine have crosses on the back like everyone's, since it's hard to find somewhere to buy them that actually makes these distinctions). A deacon should not have an icon on the front, but a cross. A priest has a cross on the back as well as the front (I think it's ok for them to have an icon instead of a cross on the front, but not sure).