I think I have figured out why those colours. If you fall in the cistern and those great guys from the RNLI and Coastguard will spot them a lot easier in the dark with the spotlight.
Tut, tut, Toureman, what's the world coming to? Mind you, a white one really is taking it too far - that's just spitting in the face of the ball float police. They were probably using her as an example to other prospective flaunters of the WC Rules and Regulations - I would've thrown away the key.