The HDR Color picker looks similar to the ordinary color picker but it has a few additional properties.
The current Brightness of a color can now be increased to more than 1. This will create an area of whiteness at the top left of the color selector, as would be expected.
If you click on Tonemapped preview you can obtain a preview of the color that will be produced. Set the Tonemapping Exposure value to the value you have set in the Tonemapping script attached to your camera (in this example 2.2).
The HDR color is also shown in the box at the top of the HDR Color picker with the falloff colors shown to the edge of the box.
HDR colors can be saved as presets just like ordinary colors. They are marked in the presets list with “h” to indicate they are HDR.