colour scheme
Visually appealing web pages need a consistent colour scheme. Without colour, a page can lack personality. With a consistent and balanced colour scheme, a page can have a consistent and balanced personality. Too much colour, or erratic colour, gives a page a confused personality.
For example, Apple.com uses different colours in different sections, but the colours are used in a similar way. In this case, the consistency derives from the treatment and application, rather than the colours themselves.