Use the color menu, accessed by selecting Color on the image menu or the selection menu, to make various changes and adjustments to image colors:
Adjust opens the Adjust Color window, where you can change the brightness, contrast, gamma, hue, saturation, and lightness of the image as a whole.
Adjust by Zone opens the Adjust Color by Zone window. Controls on this window allow you to divide an image into any number of color intensity zones (i.e. darkest to lightest), and to apply different color adjustments to different zones.
Equalize causes Easel to redistribute the colors in the image to create more balance. This is a toggle: when an image has been equalized, this item will be checked, and you can undo it by clicking it again.
Remove Redeye+ is for correcting redeye and other reflective distortions (hence the +). After you click it, drag an ellipse roughly over the distorted area; when you release the mouse button, the Remove Redeye+ window appears for more precise correction.
Transparency opens the transparency menu, for designating 1 or more colors in the image as transparent.
Grayscale and Black & White convert the image. These are also toggles; the conversion can be undone by selecting them a second time.