Hello 卡丁人,
There is no Color Gallery in Web Designer. However, you can create and edit named colors in the Color Editor (Ctrl+E), and on the color line (right click on the named color, which is reprecented as a square, and you'll see options to Edit and Rename it).
The main reason to have a Color Gallery is the ability to easily work with multiple palletes. This is especially useful if you use Pantone or other special palletes with a huge number of colors. Web site creation does not require such a huge palletes so the color line with color editor are sufficient instruments to work with.