Today’s Question: Lightroom Classic [as well as Adobe Camera Raw] has a slider for Tint (green/magenta) which is one of the pairs of opposing colors on the color wheel. It also has Temperature which is for blue/yellow. But there is no slider for the third pair of opposing colors on the color wheel (red/cyan). Why is that? Wouldn’t it make more sense to have a slider for each primary pair of opposing colors on the color wheel?
Tim’s Quick Answer: There is no need to have three sliders in order to be able to achieve any desired shift in colors. If, however, you prefer to work with three sliders rather than two, you could make use of the Tone Curve adjustment in Lightroom Classic.
More Detail: While there are three primary colors (red, green, and blue) in the context of a digital image being optimized using software such as Lightroom Classic and Adobe Camera Raw, there is no need to actually have adjustment sliders for all three of those channels.
A color wheel is a common tool for displaying the full range of color hues that are available within the visible spectrum. The color wheel forms something of a rainbow going around in a circle.
When you are shifting the color balance in a photo, you are effectively moving all color values for a photo in a particular direction toward a specific color. For example, the Temp (or color temperature) slider causes pixel values to shift in appearance between more blue versus more yellow.
In this way you can think of a color balance adjustment as representing a shift in direction across the color wheel. If you could only shift color values along a single axis across a color wheel, you would be very limited in the type of color adjustment you could apply. This is why software does not employ a single slider for a color balance adjustment.
With two sliders you can adjust colors in any desired direction across the color wheel, with movement along two axes. Imagine that these two axes are aligned with one that allows movement up and down, and another that allows movement left and right. That would allow you to navigate to any destination on the color wheel, though not in a straight line. Instead of moving diagonally toward the top-right, for example, you would use one movement upward and another movement to the right.
Of course, some software applications make use of three sliders for color balance rather than only two. And there’s no reason software couldn’t employ more than three sliders as well. But Adobe opted for two sliders (Temp and Tint) as the primary controls for color balance in Lightroom Classic and Camera Raw. If you prefer to use three sliders, you can make use of the Red, Green, and Blue curves with the Tone Curve adjustment.