[css-color] Values in `relative-color-out-of-gamut.html` seem slightly wrong. about wpt HOT 2 OPEN

@svgeesus Are implementations expected to have interop to this degree?
If so, then there should be tests for this.

They could have.

There was a bunch of detailed work done over the last few years, some in CSS Color 4 and some in color.js, often in parallel, to really reduce sources of cumulative error like slightly-different white points, inverse matrices calculated from rounded-off values, and so forth.

In most but not all cases, the result of this was better precision but well below the level of a visual difference.

My suspicion is that browser implementers could usefully check their matrix values against the current ones in sample code which are now as accurate as we can make them for 64bit floats, and update as needed.

from wpt.

A quick glance in WebKit at least shows that they have outdated matrix values:

sample code :
https://github.com/w3c/csswg-drafts/blob/ed383b552d3c977ad18116d8038c73d2c997f5a3/css-color-4/conversions.js#L159-L161

	var M = [
		[ 0.79776664490064230,  0.13518129740053308,  0.03134773412839220 ],
		[ 0.28807482881940130,  0.71183523424187300,  0.00008993693872564 ],
		[ 0.00000000000000000,  0.00000000000000000,  0.82510460251046020 ]
	];

WebKit:
https://github.com/WebKit/WebKit/blob/bf9bfb5b39381e185808dedaed839b86cd4d52ec/Source/WebCore/platform/graphics/ColorTypes.h#L430-L432

    static constexpr ColorMatrix<3, 3> linearToXYZ {
        0.7977604896723027f,  0.13518583717574031f,  0.0313493495815248f,
        0.2880711282292934f,  0.7118432178101014f,   0.00008565396060525902f,
        0.0f,                 0.0f,                  0.8251046025104601f
    };

from wpt.