It's all about consistency - the distilleries & blenders believe that consumers would be put off if the colour of their favourite tipple changed colour from batch to batch. They are probably right, at least in regards to the average purchaser of whisky.
A lot enthusiasts, here and elsewhere, think the use of E150 - spirit caramel should be abandoned, as it is suspected it has an impact on flavour. The distilleries on the other hand, maintains that the miniscule amounts used, can't be tasted.
Personally I don't know if its right or not - the fact is, that more than one of my personal favourites has E150 added - and they taste fine to me...
The malt maniacs has done an interesting experiment on this issue:
It has also been discussed here in the past:
Enemy # 1: Caramel