I can't stand how Photoshop loads your Swatch and Styles palettes with a whole pile of useless defaults. They gunk up a feature that should, by its very nature, be as pared down as possible. I try to keep custom palettes for the sites I'm designing because it makes my work faster and more consistent. If you're always grabbing the eye-dropper to get colors and copying/pasting layer styles, chances are you're wasting time and getting innaccurate results to boot. So what's a good Photoshopper to do?
You could select each color and style individually and delete them, like I used to do. But there's a faster solution that is so easy, you'll kick yourself. I've created two empty palettes for you. Just download them and follow the directions below.
To empty your Swatches palette: Open the Swatch palette, select the More Options dropdown in the upper right, and select Replace Swatches. It'll prompt you to browse for the new palette. Choose empty_swatches.aco. It replaces the default rainbow of colors with a single swatch of black.
To empty your Styles palette: Open the Styles palette, select the More Options dropdown in the upper right, and select Replace Swatches. It'll prompt you to browse for the new palette. Choose empty_styles.asl. It replaces the default monstrosities with a simple "no styles" style.
That's it. Quick and painless. When you've built your fancy new custom palettes just go back to the options menu in the upper right and choose Save Swatches/Save Styles. Once you've saved them you can load them into any document you want.
UPDATE: If you're on CC, there's a new little line of colors above your palette. These are not actually "swatches" - these are the 16 most recent colors you've grabbed with the color picker. They won't save out as part of any saved palette. There appears to be no way to get rid of them, so just avert your eyes.