Amyloplasts – Amyloplasts are the greatest among all 3 and they store and synthesize starch.
Proteinoplasts – Proteinoplasts help in storing proteins required by the plant and can be typically found in seeds.
Elaioplasts - Elaioplast also helps in storing fats & oils which are needed by the plant.
Leucoplasts are in general colourless due to the absence of any pigments. They seem to appear purple only if they are stained with iodine or any other dyes.