Colour is not a property of electromagnetic radiation, but rather a characteristic of visual perception.
The human eye, and therefore human perception, is sensitive to the range of light wavelengths that constitute the visible spectrum, including the corresponding spectral colours from red to violet.
Light, however, is rarely of a single wavelength, so when an observer notices a red ball they are probably seeing a range of similar wavelengths of light within the visual spectrum.
Perception of colour is a subjective process as our eyes respond to stimuli produced by incoming light but each of us responds differently.