lawngreen or 7CFC00 ?
mediumblue or 0000CD ?

Readability is increased, but you loose some fine-control and it (only?) works since  IE 6 (W3C Validator complains !?)

Its great when just building a mock-up: writing brown+olive+x is faster/easier than getting some hex values.
For professional designs, the 140 CSS Colorcodes colors are too limited, but for your everyday Webblog its ok 😉