The Sodium Hydroxide (NaOH) solution is an alkali. Because of the dissolved sugar, it settles to the bottom of the cylinder. The acid floats on top as it is less dense.

The clever bit is using the Universal Indicator solution. Universal indicator is red in acid, green in neutral solutions, purple in alkali.

You might have noticed that when the acid and base meet, they cancel out each other leaving a green coloured neutral solution in the middle. So a base is an acid opposite.