In Example 20 in the section https://drafts.csswg.org/css-color/#serializing-color-function-values, the following results incorrectly puts a % sign on the alpha serialization.
is the string "color(prophoto-rgb 0.28 0.403 0.423 / 0.85%)", if three decimal places are retained.
The alpha value should be just 0.85 (I think. I can't quite tell where it states that alpha is serialized as and not a percentage for color functions, but since all the other values do, it should probably should as well).