Why the colour scheme for BS951 earth clamps?

[ringer]

Can anyone explain to me why we have different colour earth clamps?
I know that red is for dry environments, blue for damp/corrosive and green same as blue but for larger diameter earth wires.
Why can't we use a single colour for all environments, the clamps appear to me to be made the same?

 

[Sintra]

Always just use blue or green as they suit all conditions all i can think of is that they are made of a different type of material.

 

[SirKit Breaker]

Sintra is right they are graded to suit whatever environment they are used in, but dont ask me which is for what cos i cant remember

 

[not clever]

http://www.legrand.co.uk/en/en/liblocal/pdf/Earth clamps.pdf