When you extract a key to isolate a colour, you can view it in the Player. Keys are based on the chrominance and luminance of a selected colour from the original image. Once you have selected a colour, you then set the tolerance and softness ranges by sampling the original image. Tolerance defines how similar luminance and chrominance values will be keyed (made transparent) in the secondary. A higher tolerance setting extracts a broader range of luminance and chrominance values, while a lower setting extracts a narrower range, leaving the rest of the image untouched. Softness defines how similar luminance and chrominance values are softened (made partially transparent) for the secondary. A higher softness setting extracts a broader range of luminance and chrominance values, while a lower setting extracts a narrower range, leaving the rest of the image untouched. You can soften the edge of a key to blend the secondary colour grading with the rest of the image.
Keys are, by default, based on original scans, bypassing any input primary colour grading. This allows you to modify an image upstream of any secondary without changing the key. For example, after you key a secondary, you can safely perform a hue shift from the Curves menu. The key, based on the original image colour, is unaffected. To base a key on colour corrected sources, enable the Src: Prim (Source Primary) button.