onXyz method Null safety
Creates chalk with background color defined from XYZ color space parameters. https://en.wikipedia.org/wiki/CIE_1931_color_space
Implementation
Chalk onXyz(num x, num y, num z) {
var rgb = ColorUtils.xyz2rgb(x, y, z);
return makeRGBChalk(rgb[0], rgb[1], rgb[2], bg: true);
}