Click on the color slider icon, and then choose "RGB Sliders" from the drop-down list.
You can also use the magnifying-glass as a color picker to pick up an exact color from anywhere on the screen; also see @ken's excellent comment below clarifying how colorspaces work with the magnifying glass.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…