According to the spec:
When Enter is pressed in the custom color popup dialog
Dismiss the dialog. Save the new color to the Custom Colors area in the Color Palette. Close the Color Palette. Update the Color Chooser. Apply the color.

But I cannot understand, how to reach this key usage, because, there are controls on the scene (of custom color selector), which are initially focused, so I cannot use enter in a free way, to confirm chosed color.