In some countries it's seen vandalism to deface or alter the flag, but then if you changed the colours of something like the French flag, it'd just look like three coloured stripes and you couldn't really tell it's a flag.
Well you would, but it's more difficult to use different colours on a tricolour - so many colours are out of bounds as another country has them:
http://en.wikipedia.org/wiki/Tricolour#Examples Change the white to yellow and it's Romania, change the blue to green and it's Italy's etc
As long as they're not burning it, I don't really mind what people do with the flag, although it looks a lot classier in green - the red and blue version looks so trashy, especially when used on TV, like in the BBC's Eurovision selection shows, it just lowers the tone somehow (if that's even possible with Eurovision).
Although the 2012 logo looked better in red white and blue!