A round bottom flask was affixed with a reflux condenser, drying tube and addition funnel then charged with dimethylmalonateand sodium methoxide.

The solution washeated to boiling with stirring. The heating mantle was removed andmesityl oxide was added dropwise to the reaction mixture. The reaction mixture (light brown color) was gently refluxed under heat for one hour until all standing liquid was gone. The condenser tube was removed and the solid residue, still moist, was left to thicken under heat.

The reflux apparatus was reassembled and 3 M NaOH was slowly added to the round bottom flask containing the thickened reaction mixture. The resulting reaction mixture was refluxed for one hour and transferred to an Erlenmeyer flask. 6M HCl was added to the flask. The mixture turned yellow immediately.

A watch glass was placed over the flask and the mixture was heated to boiling. During boiling the mixture turned darker with dark droplets noted on the bottom. After the heat was removed the reaction mixture was cooled to room temperature.

A dark yellow layer formed on top of the reaction mixture during cooling. The mixture was vacuum filtered to yield a solid.

Please explain the color changes in bold - the chemical reactions, why color changed, etc.