Some colours are more taxing to look at than others. Bright colours reflect more light which sometimes over stimulates the eye. A page with a splash of light yellow or bright orange may attract the eye, but unrelieved light yellow and bright orange will be off putting as the eye becomes tired. The eye is confused by contrasting colours. For example, when there is not much light, blue and green appear brighter than reds of equal brightness.
Colour psychology is back in fashion.
The fashion industry has taken full advantage of the resurgance of this. For example, look at the Colour Me Beautiful fashion programme. Back to the point in question, web design and colour. If you've had a think about what colours you want to use on your site you may have some problem actually conveying these colours to others because of the shortcomings of the equipment you and they are using. Our monitors appear to show a full range of colour.