The gradient section of the area style dialog has two color settings, both implemented as dropdown control. These controls show the color but not the label as in the solid colors section, for instance.
Running on Linux/KDE and compiled for KDE (--enable-kde4)
Selecting one of the predefined gradients (e.g. Tango Green) adds the color as user-defined to the palette. Not sure that the gradients aren't defined independent from the standard palette. In this case we should consider to use other colors.
Most of the colors(From and To) used to create gradients are not available in LibreOffice standard palette. Hence it appears as undefined color without a label.
@UX: The color dropdowns at gradient (and hatching) do not show non-standard color names (like "Red" or "Tango Sky Blue"). And most of the gradients do not use standard colors, such as "Tango Green". It looks like a bug compared to "Sunset", for example. Shouldn't we change the colors so that the presets are defined by colors from the standard pallete?
No comment sounds like everybody is fine with the current state. Closing this as WFM.