Thank you all for your opinions. As far as I can tell at least one person likes each option - lol.
A couple of thoughts as I read through the comments. I made a decision to only use ivory coloured thread. Where this is used as a topstitch on the red or green it gives quite a casual look, as does the multi fabric.
The suggestion to use a mixture of buttons to echo the mixture of fabrics did appeal, so I'm going to hunt through the bags of odd buttons and see if I can find enough of the same size, but in different colours.....