White Balance—controls the 'temperature' of the image. In the Develop Persona this is measured in Kelvin (K). Drag the slider to the left to cool the image, or drag the slider to the right to warm the image.
Tint—tints the image either towards magenta or green. This is useful for removing color casts, especially if the image was taken under artificial lighting (e.g., tungsten or fluorescent).
Picker—allows you to sample the image to set the white point on which the white balance will be calculated. You can sample using one of the following methods:
Click to sample a pixel under the cursor.
Drag the cursor across the image to sample all pixels under the cursor. The averaged color from those pixels is used.
Press the and drag to sample under a rectangular marquee, again using the averaged color of those pixels.