How does Benedict's solution change colour?

Benedict's reagent (also called Benedict's solution or Benedict's test) is a reagent used as a test for the presence of mono saccharides (such as glucose and fructose); it is also used for some disaccharides like maltose, or more generally for the presence of aldehydes, in a solution.

This video show Benedict's solution being used to test for the presence of sugar in solution.

Benedict's solution, deep-blue alkaline solution used to test for the presence of the aldehyde functional group, −CHO. The substance to be tested is heated with Benedict's solution; formation of a brick-red precipitate indicates presence of the aldehyde group.

Benedict's reagent contains blue copper(II) ions ##Cu^(2+)## which are reduced to copper(I) ions ##Cu^(+)##. These are precipitated as red copper(I) oxide which is insoluble in water.In this process aldehyde group is oxidized to Carboxylic acid.