They were not really using uniforms. The soldiers were mostly "mercenaries", people hired to fight. They had their own equipment, although sometimes a country would pay their soldiers in wargear instead of food or money (if they got to pay them). At least, the king of Spain did that at some point.
But, as far as I know, armies didn't have regular uniforms. There could be a distinctive colour of the rank, the army (like the flag) or the company (the Spanish army in Flanders had a company made of old brigands and bandoleros, called the Papagayos, the "Colourful Parrots", because as brigands, they used to wear fancy and colourful clothes and feathers, and they obivously kept their equipment when entering the army.
