The term 'Spectral Colour' refers to a range of colours that can be seen in the visible spectrum. The term is often used to describe a range of hues that are softer and more muted than other colours. The crossword solution for this term is 'PASTEL', which is a type of colour that is usually light and soft, often with a hint of grey or white. Pastels are often associated with spring and summer, and are commonly used in art and fashion.