This is the standard viewer color picker, used for tinting objects.
The large “rainbow” square on the right allows you to directly click on a color to select it. Immediately to the right of that is a brightness strip, allowing you to fine tune the color brightness.
Alternately, you can specify an exact color in RGB, by typing in the values in the Red, Green and Blue fields. Or you can give the color in Hue, Saturation and Luminosity form.
Note the 3 tabs. These allow you to also specify colors in LSL format, or in HEX (HTML) format.
The rectangle on the left shows the currently selected color. If you wish to save this color for larter use, click and drag it into one of the smaller rectangles below. These are mostly prefilled with standard values, but the four at the right end are white and designed for saving your own selections.
Another way of selecting is color is to use the dropper tool. click that, then click on any in-world objec to “pick up” the tint from it.
If Apply now is enabled, color changes made here will be immediately visible on the object you are editing.
Once you have finished making changed, click Ok to apply them; click Cancel to revert to the original color.
If you wish to obtain an LSL color vector, click on Copy LSL; this will copy the LSL color vector into your clipboard. You can then paste it into a script.