Not all Color fields will support HDR values. If you're using a field that you do not control the code of and it does not have a HDR color picker, then it's unlikely it was ever intended to take HDR values.
Mark the field with the ColorUsageAttribute, with hdr enabled:
Unity, huh, how?
[ColorUsage(true, true)] // showAlpha, hdr
[SerializeField] private Color myColorValue;