When cooking veggies, you'll notice a color change from dull green at the raw stage to bright green at the peak of chlorophyll activation to olive green after prolonged cooking.
Chlorophyll is the compound responsible for making vegetables green, and the magnesium core within the chlorophyll becomes displaced by hydrogen in an acidic environment.
Neutralizing the acidity of the water with baking soda can slow down this shift to keep the color brighter. This also works for other veggies like cabbage, tomatoes, and onions.