I have heard quite a bit of different things concerning colours on armour clothes and i wanted to check if someone might know. Some say all arming clothes where of natural colour cos no one would bother with colouring something that will get so dirty, and that is essensically just a functional peice of clothing. Maby it was so that linen never was coloured just cotton? And if so can you really make something out of cotting that will stand the abuse of a chainmaille over it? Or was it maby a difference in the times - almost exclusively see coloured doublets/aketons for the late 15th C but almost all pourpoints of the late 1300 and early 1400 seems to be recreated in the plain, linen colour.

Any tips or thoughts on this matter please advise.

The problem is that there aren't a lot of surviving arming clothes to analyze. There are a couple of fantastic surviving coat armours (that of the Black Prince and Charles VI), but those were likely worn over armour. Those were covered in silk or velvet and were brightly colored. Both date to the latter half of the 14th century.

Dyes were supposedly expensive, though, so it has been thought that many could not afford them and that those who could often used them in garish colors often, but not always, coinciding with heraldic colours.

I would think at least some aketons of the 14th century would have been coloured, since many effigies show the jupon and haubergeon both being cut so that the dagged aketon beneath would be clearly visible (all three layers are visible). Of course, effigies typically aren't in colour, so it's hard to say for sure. My thought is that they wouldn't have gone to the trouble to make the aketon visible if it weren't nice-looking.

Heard somewhere in a discussion that many gambesons and acetons where boiled in salt and wine (don´t know why?) and if that was true and if it was red wine it would have made a pink/purple coulour on the fabric, wouldn´t it?

Some dyes would be expensive - murex purples or anything resembling a true black, for example. However, many dyes can be made from common materials such as barks, fruit, minerals, &c. If you want to experiment, try http://www.pioneerthinking.com/naturaldyes.html