The reasoning behind the choice of colours was so as not to have them confusable with the other major systems that were in use at the time of the change over. They're also easily identified if you're colour blind dark = hot, light = neutral, stripy = ground.
As for plugging a european applience into a US 240V (2 x hot) outlet.
There are a few problems:
1) European appliences tend to be designed for 220-230V not 240-255V (old UK appliences might fare better). For all european countries, excluding the UK and including Ireland, the voltage was 220V 50hz for many many years. The UK standardised on 240V 50Hz (along with Malta and Cyprus). A decision was made to move to 230V (nominally) to bridge the difference. You might find that EU appliences connected to a US 240 supply might be running a little strangly.
2) They are designed to have a reference to 0V ground. Many appliences with electronic components, particularly computers, can have quite serious problems when used on an old 127+127V supply in Europe so I doubt they'd be very usable on a US split phase supply either.
3) as mentioned already the frequency difference would be a major problem.
