The colorization algorithm takes whatever colors are in the skin and replaces their hue
with the one from the color you provided. This, however, does not change the saturation and value. Therefore, all shades of gray are not colorized. And since the Default skin is all-gray, it will not be affected by any colorization. The editor icons may be affected, if they have colors. This is also the point - You wouldn't want the Black skin to turn green, you might only want to change its highlights.
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