Err, that should be 'red', 'yellow', 'double yellow', 'green' of course, in order of most restrictive to least restrictive aspect. I switched yellow and double yellow around...
Since I'm correcting myself anyway, for the benefit of a few people who seem to think that the LGV lines use illuminated signals, they do not - signalling is presented in-cab, and for bloody good reason.
High-speed trains take a long time to stop. This means you either need (a) very long signal blocks, so that the distance of the block is adequate for the train to slow down when it meets a restrictive signal, or (b) you need more signal indications, allowing you to slow the train down in smaller steps. Longer signal blocks means fewer trains on the lines (== reduced capacity) so there are tradeoffs to be made here.
The standard on British high-speed lines is 4-aspect signalling. Red-yellow-double yellow-green as described above. "Green" means 'go at maximum line speed', "red" means stop, and the yellow/double yellow in between are speed grades in between.
When the IC225 trains (max speed ~ 140mph) were introduced on the East Coast Main Line, BR's solution to allowing them to reach their maximum speed was to introduce a fifth signal aspect - the 'flashing green' signal, rather than reduce capacity across the entire line by lengthening the signal blocks (not to mention the inordinate expense of resignalling the entire route like that.)
It was then decided that in practice drivers could not be expected to respond to trackside signals at over 125mph, and the fifth aspect was abandoned - for this reason the ECML IC225s have never actually run in service at their top speed, and are limited to 125mph. From that point on it was mandated that for higher speeds the signalling must be presented in-cab.
Now, the point of this little anecdote is this - on the LGV lines, the same capacity/signal block length tradeoffs need to be made, but the problem is even more acute because the trains run even faster. So the solution is the signalling has even more aspects - something like 7 different signals between 'maximum line speed' and 'stop'. These are presented in the cab of the train as a target speed, rather than a colour.
So you see, the idea of trackside signalling something like this is nuts. You'd need a signal pole with a ridiculous number of lights on - 'flashing mauve', anyone? - so, no, it's not quite as simple as "Now you might think in an emergency like this you could drive a little slower and even use an extra driver in case one could not see a big bright red light in the pitch black." A train with in-cab signalling is something of a requirement.
On another note - the reason this isn't a problem in Canada is that (a) you could outrun a Canadian train with a camel and (b) the cost-benefit calculation for dealing with something that happens every day rather than every 15 years is rather different.
And bad as the weather here is, we don't get a lot of snow in summer, so probably no great danger to the Olympics...