Key any color with the Chroma Keyer and work in HSL space to create masks on hue, luminance, and saturation. When you have a contrast between two parts of an image, likely a keying technique exists to separate them.
Keying tools like the Delta Keyer and Ultra Keyer work best on traditional keying scenarios like green screen and blue screen. You can use them with other background colors, however, they have issues separating colors that are close, like orange and red.
In those cases, the chroma keyer may give a better result. Frequently, when we want to make arbitrary color selections, the biggest distinction between two parts of an image may not always be in the hue of the color but could be in saturation or luminance.
In those cases, a keyer that works on RGB values may not yield the best results. Instead, you can work on Hue, Saturation, and Luminance (HSL). This is what the HSL Qualifier on the color page of DaVinci Resolve does.
Creating your own HSL Keyer in Fusion is easy. A color space transformation brings the RGB image into HSL space. There you can apply a regular Chroma Keyer to select areas in the HSL image.