Get darker color hex code for given color hex code

How to get darker color hex code for the given color(represented with hex code).

For example, for given color #999999 i want to get darker hex color, namely it can be #666666, because #666666 is darker than #999999, and 开发者_运维知识库they are GREY

Another example, for given orange color, I want to get darker orange color hex code.

Assume we use ActionScript 3.

Depending on what you are after, you may have better results by working with the HSL color space and adjusting the L value. This is what the color picker in the Flash authoring tool does when you lighten/darken a color. A little Googling will dig up the forumlas and code for converting RGB to HSL and vice versa.