What is the "blue spirit" (or "red spirit") in mercury-free thermometers?
As per the Wikipedia page on Spirit Thermometers:  


  The liquid used can be pure ethanol, toluene, kerosene or isoamyl acetate, depending on manufacturer and working temperature range. Since these are transparent, the liquid is made more visible by the addition of a red or blue dye. 


1,4-bis(butylamino)anthraquinone - commonly known as "Oil Blue 35" - may possibly be used as the blue dye.