Semiology of crisp packets

Note to Yanks:
crisps = potato chips
colour = color
flavour = flavor

I was wondering recently, why it is that certain colours correspond to certain flavours. Obviously in some cases the colour goes with whatever the flavour is meant to taste of. But in other cases it seems fairly arbitrary. I think crisp packets should be a good example to follow.

The three most common crisp flavours are ready salted (e.g. normal, no flavour), salt & vinegar (e.g., vinegar) and cheese & onion (which I strongly believe has salt in it as well, they just don't mention it). In Walkers' crisps, ready salted is indicated by a red packet; salt & vinegar is green; and cheese & onion is blue. Why is that? What do these colours have to do with the flavours of the crisps? Shouldn't cheese & onion be yellow? Ready salted red looks like it's tomato ketchup flavour. Shouldn't it be... I don't know... fried potato colour?

A lot of other companies are bought over by Walkers so they of course have the same colour scheme. But others, such as McCoy's, have a different but similar scheme: the colours are the same, but cheese & onion is now green and salt & vinegar is blue. This makes a sort of sense... salt usually has the grand name of "sea salt" on most packets, and the sea is usually blue. But green is a fairly unappetising colour to associate with cheese, isn't it?

Just throught it was strange - the same three colours are used despite their irrelevence, but, with equally no reason, some companies switch two of them around. Could lead to confusion and unusal taste sensations.