当颜色不再需要时，这样为我们省去了清除它的麻烦，因为颜色管理器会负责颜色的清除。
This saves us from having to dispose of the color when it is no longer needed, as the color manager will care about disposal.
该模式不清除任何颜色或深度缓存。
This mode does not clear either the color or the depth buffer.
红色是很难清除的颜色。
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