There’s nothing like a gorgeous sunrise or sunset full of color… unless your image shows a bunch of horrible color banding in the sky.
The HSL (hue, saturation, lightness) tool in Lightroom and Photoshop is an excellent way to boost the saturation of a colorful sky, but it needs to be used correctly. Simply boosting the color saturation is likely to create artifacts in the sky known as “color banding”.
It’s unlikely that you’d ever create something that horrible without noticing, but it’s a problem even when it is too subtle to notice. Even if it doesn’t show up right away on your monitor, it might easily become more apparent after further processing in Photoshop or when you print the finished image. Or, you might run into it and decide to boost the sky a bit less to avoid the issue, when you could have gotten the color you wanted without banding.
Both Lightroom and Photoshop can run into this problem, and there are good ways to avoid the issue in both programs. While the tools are designed differently, the basic approach is to ensure some inclusion of adjacent colors. Temporarily over-saturing to identify and address any banding is a helpful technique, as issues that are subtle now may turn out to be more problematic after further processing or printing.
How to use HSL in Lightroom and avoid banding:
Lightroom offers 8 color saturation sliders in the the HSL panel. Each one covers a fixed range of colors, and that’s where banding becomes a problem. A colorful sky isn’t just one color, it’s usually a mix of blue, purple, magenta, red, orange, and yellow. Sometimes aqua. Pretty much everything but green, unless you have a rainbow or storm. So almost any color might be relevant. Typically, your sky probably has 2-4 colors. To avoid banding, you just need to make sure you adjust all the relevant colors.
When you look at the colors in the sky (or use the targeted adjustment tool to help pick the colors), you’ll probably see 1-2 colors that dominate the image. Those are the key ones to adjust, but you typically need to adjust the adjacent colors a little bit to allow a smooth color transition to avoid banding. So, if your sky is mostly orange (like the example above), you should tweak red and orange as well. When it bleeds deep in to the reds (like the top of the image), you should adjust magenta (red and magenta are adjacent colors, when you hit the top or bottom of the color sliders in Lightroom, you need to mentally jump to the other end of the list).
To identify if banding is an issue in your image, push the color slider you want to adjust to the far right. Go beyond the amount of color you really want, because it is easy to see issues when you push to the extremes. You can then adjust the adjacent sliders until you see no banding and a good balance. This will be oversaturated, but you will know the relative adjustments needed to avoid banding. Now just bring all the sliders down proportionally to get to the saturation you want to see in the image.
How to use HSL in Photoshop and avoid banding:
Photoshop also uses predefined color ranges, but the HSL tool in Photoshop is less prone to banding for a couple of reasons. First, Photoshop splits the color wheel into 6 colors, so each one is a little more broad. That larger range of adjustment automatically helps minimize banding. Second, Photoshop lets you precisely adjust the color targeting and feathering at the edges of the color selection.
The easiest way to adjust in Photoshop is to use its targeted adjustment tool (hand icon) to click and drag from a color in the middle of the range you wish to adjust. This will automatically select the right color. Bring up the saturation until the primary color looks a little too saturated, and then tweak the color selection range until you see no banding and a good balance, and then bring down the saturation slider until you achieve the desired saturation.
Ultimately, you can get excellent results and avoid banding with either tool. Photoshop is less likely to create banding when moving a single slider, and the ability to customize the targeting or use layer masks ultimately makes it a more powerful and flexible tool.