After enquiry, the following useful information was obtained:

Because Islay is rich in peat, the degree of malt smoke is much stronger and exceeds that of other whiskey producing areas.

Peat is one of the reasons why different distilleries have different flavors in their whiskey. Peat smoke contains a substance called "phenol". These phenolic substances will be absorbed by barley malt during the smoking and baking process. This is the principle of "the one who is close to vermillion is red and the one who is close to ink is black".

It can be seen that everything about Islay whiskey, including the color of the bottle, is related to the abundant peat in the area.