You can use the controls in the HSL / Grayscale tab to adjust individual color ranges. For example, if a red object looks too vivid and distracting, you can decrease the Reds values in the nested Saturation tab.

The following nested tabs contain controls for adjusting a color component for a specific color range:

Hue

Changes the color. For example, you can change a blue sky (and all other blue objects) from cyan to purple.

Saturation

Changes the color vividness or purity of the color. For instance, you can change a blue sky from gray to highly saturated blue.

Luminance

Changes the brightness of the color range.

If you select Convert To Grayscale, you see only one nested tab:

Grayscale Mix

Use controls in this tab to specify the contribution of each color range to the grayscale version of the image.