A large molecule in the flask. Besides it has a deep blue color, it also acts as a pH indicator. When it’s in a basic media, or pH over 8 it has a deep blue color (as seen on the picture), but under that it is bright red. 

Did you know that while water has a pH 7 when neutral at room temperature, but if you heat it up the pH decreases.
Why? pH can be defined as the chemical potential (mu) divided by thermal energy (kT). This fact is clearly evident when we measure the pH of water at 0 deg C we find it to be 7.47, but the same water at 100 deg C will have a pH of 6.14! Heating up water more will decrease it’s pH more and more, it could even go under 1 under high temperatures and pressures.

In chemistry, pH is a numeric scale used to specify the acidity or alkalinity of an aqueous solution. It is the negative of the logarithm to base 10 of the activity of the hydrogen ion. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are alkaline or basic. 

What causes the pH? This: 2H2O(l)⇌H3O+(aq)+OH−(aq)

pH 7 is 0.0000001 mol/dm3 concentration of H3O+ ions and pH2 is 0.01 mol/dm3 concentration of H3O+ ions.