Combine 1/2 teaspoon of soda ash, 1/2 teaspoon of liquid dish soap, 4 tablespoons of white vinegar, 2 tablespoons of lemon juice and 2 cups of hot water inside a spray bottle. Mix the components well until no sediment remains on the bottom of the bottle.
Spray the white veneer shelves with the cleaning solution. Thoroughly saturate the yellow areas. Pay special attention to darker areas or spots where the yellowish grime is thickest. Let the solution soak in for 10 to 15 minutes.
Dip a sponge in very hot water. Wring out the excess liquid. Scrub the white veneer shelves in a circular pattern. Remoisten the sponge as needed, since the heat from the water will help lift the grime.
Wipe up the lifted grime, using a coarse washcloth. Spray down the cabinets again with the cleaning solution. Immediately wipe the cabinets clean with the coarse washcloth to lift up any remaining residue.
Repeat Steps 1 through 4 as needed until the shelves reach their original shade of white. Perform light cleanings every couple of weeks to maintain their color and cleanliness.