Re: [csswg-drafts] [css-color-4] rgb-to-hsl source code produced hue NaN when rgb values are equal (#8304)

Yes, this is as expected. The hue is [powerless](https://drafts.csswg.org/css-color-4/#missing), which is represented in CSS with the keyword `none` and in code with the value `NaN`. 

> For example, in [hsl()](https://drafts.csswg.org/css-color-4/#funcdef-hsl), the hue component is [powerless](https://drafts.csswg.org/css-color-4/#powerless-color-component) when the saturation component is 0%; a 0% saturation indicates a grayscale color, which has no hue at all, so 0deg and 180deg, or any other angle, will give the exact same result.

If such a color value is converted to another color space, [the value `0` will be used for the missing value](https://drafts.csswg.org/css-color-4/#color-conversion). However, if two colors are interpolated and one has a missing value while the other has a valid value for an analogous component, then [the missing value is taken from that second color](https://drafts.csswg.org/css-color-4/#interpolation-missing).

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Received on Thursday, 12 January 2023 16:41:07 UTC