The Tuning controls work differently than controls on the Basic Fixes and Effects tabs. All tuning adjustments are treated as a single edit and are reversed by clicking one button: Undo Tuning. Use the Tuning tab to apply multiple edits or adjust an already edited image. When done, click another tab or the Back To Library button.
Magic Contrast. This is the same as the Auto Contrast button (Basic Fixes tab).
Magic Color. This is the same as the Auto Color button (Basic Fixes tab).
Fill Light. This is the same as the Fill Light control (Basic Fixes tab).
Highlights and Shadows. When used together, these controls enable you to manually adjust an image's contrast and brightness.
Color Temperature. Move this slider to adjust a picture's "warmth." Drag to the left to make it cooler or to the right to make it warmer.
Neutral Color Picker. Click the Eyedropper icon and then click a gray or white area in the image. Doing so sets that color as neutral for the image, allowing Picasa to automatically adjust all other colors.