You can have more than one palette open in the Colour Palette at one time:

In this illustration, there are three colour palettes available: the Default tab containing the standard colours displayed in the Colour Palette; two custom palettes named Custom 1 and Custom 2. You can change the name of the custom palettes and add as many colours as you require to each.

To open a different palette, simply click on the tab name and the colour wells in the palette will be displayed.