Why is colored alcohol used as the liquid in a weather thermometer rather than mercury?
Mainly cost and danger.
Mercury is not only way more expensive than the (higher) alcohols used in thermometers, but it is also very poisonous and bad for the environment (heavy metal).
The silvery mercury column is also harder to read as compared to a coloured column.
At very low temperatures (-39 C) it solidifies, while alcohols don't.