The time needed for the dye is irrelevant for the question of the unit outfitting. At the wars beginning most cloth was not produced and dyed on order but for stock.
For those who had to equip a force it was important what was availabe and what was the price of it. Strangely for centuries quality was not considered very important, so soldiers got clothing that lasted for weeks only.
The best price was getting the stuff for free. Plunder or war taxes (another word for plundering) from towns produced the cheapest. Next best was a seller in a situation that forced him to sell cheap to one party.
Great cloth producing centres had large stocks of cloth and often stocks of ready made coats and trousers too. A unit that came near such a centre would have got the stuff that was ready irrespective of the colour or cut.
I takes a good administration to supply an army with stuff of a certain style and colour for a longer time. Preorder takes money or credit and the option to transport the stuff to the units.
The King's war government in Oxford tried a lot but London was in a far better situation to do that.
Anyway, imagin going out for 3 months in a set of cloth. Marching half of the time. Sleeping in your dress. No laundry machines, rain, mud, diarrhoea, what will your dress will look like?