The image you have been working with is slightly underexposed. You can quickly adjust the exposure of the image with the Exposure slider.
1.
In the Adjustments Inspector, drag the Exposure slider in the Exposure adjustment controls to the right. You will notice a vast improvement in the image exposure.
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Tip
To reset a filter back to its default, simply click the Reset button (the curved arrow pointing left) on the right side of the filter name. If you wish to temporarily disable one of the filters you've already applied, just deselect it. To completely remove all adjustments from an image, choose Action > Remove All Adjustments from the upper-right corner of the Adjustments Inspector.