WLab and color differences
Every value here is a measurement of a material's color: the responses of some sensors to the material under some light (XYZ for a CIE observer, cone or camera responses for others). The condition's Wpt normalization turns each measurement into WLab, a description of the material, and ΔEWLab is the difference between two materials, in units that behave like familiar ΔE units. It reads the same way for every observing condition: a difference of 2 means the same for a camera's measurements as for the CIE 1931 observer's. Comparing materials across different lights or observers needs their spectra; that is the Objects lab.
1. The observing condition
2. The colors
CIELAB values are turned into XYZ with the white of the observing condition above, so choose the condition they were measured in (for a D50 viewing booth: CIE 1931 under D50). CIELAB is defined on XYZ, so this needs one of the CIE color-matching observers: CIE 1931 (2°), CIE 1964 (10°), or CIE 2015 (2° or 10°), whose functions are made from the CIE 2006 cone fundamentals.
Line n of each box belongs together: a name (optional), the first color's values and the second color's. Where a second color is left out (an empty line, or no line), the first is a single color, shown in WLab only. Values separated by commas, tabs, semicolons or spaces; a header line is skipped. Columns pasted from a spreadsheet keep their lines.
3. WLab and the differences
Lw, aw, bw are WLab coordinates, cw and hw its chroma and hue angle. The chips show each color as the display color (sRGB) of its material under D65, from WLab, approximately, and clipped where they are outside sRGB.
About ΔE00 here. For the CIE color-matching observers, ΔE00 is the familiar one: from the CIELAB of the measurements in the observing condition above, with that condition's white, as a spectrophotometer or colorimeter reports it. ΔEWLab is the difference between the measured materials as WLab's reference observer (CIE 1931, under illuminant C) would see them, whatever the measuring condition. The two answer the same question only in that reference condition, where they should be close; under other lights or observers they can differ, and the gap shows how much the measuring condition changes the answer.
4. Where the colors sit and how they differ
The aw–bw plane
Lightness against chroma
How large the differences are
ΔE00 (this condition) against ΔEWLab
Each pair is an arrow from its first color to its second.