A solar cooker uses a black painted box because black:

1. Different colours absorb sunlight differently. 2. Black surfaces absorb almost all incident wavelengths. 3. Absorbed sunlight is converted to heat. 4. The black box therefore heats up faster and more strongly. 5. So black paint maximises heat absorption. _Source: syllabus Science Ch 14 'Sources of Energy' (byjus.com extract)_