[css-color-hdr] In what colorspace is `eps` = 0.001 one just noticeable difference?

Perhaps the answer is in [[ISO_21496-1]](https://drafts.csswg.org/css-color-hdr/#biblio-iso_21496-1) but I have not purchased a copy.

(W3C has an [informal liaison](https://www.w3.org/liaisons/#I) with [ISO TC 42](https://www.iso.org/committee/48420.html)/WG 23 and is establishing a Class C liaison which includes document sharing, but that has not been completed yet).