Colourless (non-pigmented) plastids found in the storage tissues of plants — such as the parenchyma of a potato tuber — are called leucoplasts. Their main job is storage, which is why the correct answer is Storing starch produced through photosynthesis.

Plastids are a family of double-membrane organelles unique to plant cells, and they are broadly classified by colour and function:

• Chloroplasts — green, contain chlorophyll, and carry out photosynthesis.
• Chromoplasts — coloured (red, orange, yellow), store carotenoid pigments that give petals and ripe fruits their colour.
• Leucoplasts — colourless, specialised for storage.

A potato tuber grows underground and receives no light, so its plastids have no chlorophyll. The starch is actually made in the leaves during photosynthesis, converted to soluble sugar, transported down to the tuber, and there re-converted and packed into leucoplasts (specifically amyloplasts, the starch-storing type). This stored starch is the plant's energy reserve for the next growing season.

The other choices describe different plastids or organelles: capturing sunlight to produce energy is the role of green chloroplasts, not colourless leucoplasts; synthesizing red and yellow pigments is done by chromoplasts; and producing amino acids for protein synthesis is chiefly the work of ribosomes and other cellular machinery, not these storage plastids.