Caveat: I am very new to this period as well. Others may come along and point out that I have spouted bollocks.
Having said that, my understanding is that this wa a transitional period regarding uniforms. European armies of the time were in general not uniformed but at some point the Swedes began to uniform some infantry regiments. Famously, they created 'colour' regiments; yellow, green, blue... There was a thread on here not so long ago with a very nice Swedish force painted like this. Also Dalauppror posts here quite often and has been showing off TYW stuff lately.
Having said that, this was a period of many mercenaries being used, I would imagine that many units, even in Swedish armies would not be uniformed.
AFAIK Swedish cavalry were not uniformed like the infantry.