Why are cotyledons white inside the seed?

Cotyledons inside the seed are white due to the absence of chloroplasts as light is necessary for the synthesis of chlorophyll. The cotyledons inside the seed are not green because the cells in these contain leucoplasts. When the cotyledons come out of the seed during its germination, these are exposed to light that leads to the biosynthesis of chlorophyll. The leucoplasts are converted into chloroplasts due to synthesis of chlorophyll and the cotyledons turn green.