Open a CxF color file (the ISO 17972 format that spectrophotometers, ink kitchens and color libraries export) and see what's inside: every color's spectral curve, its Lab under different lights, the measurement conditions side by side, and CMYK through your printing profile. The file is read in your browser and never uploaded. Theory: CIE 1931 and XYZ →
Convert's Find nearest can search these instead of huebic's PANTONE screen values. They stay on this device; remove one with ×.
CxF (Color Exchange Format, ISO 17972) is how measuring instruments, ink kitchens and color libraries pass colors around. Each color can come with its spectrum: how much light it reflects at every wavelength, from violet to deep red. It may also carry the Lab values the instrument worked out, and a CMYK or RGB recipe.
Your file stays on your device: huebic reads it in the browser and keeps nothing.
Lab is one answer for one light. The spectrum is the color itself, so huebic can work out the Lab under any light: D50 (how print is judged), D65 (daylight), A (a tungsten bulb). The swatch shows the color as your eye sees it after getting used to that light; the Under other lights table shows how far it shifts. Two colors that match under D50 but drift apart under A are a metameric pair, a classic print and packaging headache.
The observer is the standard human eye: 2° for small samples (most color work), 10° for larger areas such as paint and textiles.
These are the measurement conditions of ISO 13655, which say how much UV the instrument's light contains. That matters because most white papers contain optical brighteners that glow blue under UV.
M0 is the old tungsten-like light with an unknown amount of UV. M1 is D50 with a defined UV share, the current standard for papers with brighteners. M2 cuts the UV out. M3 is M2 plus polarising filters, for wet ink on press. When a file holds several conditions for the same colors, the table shows the difference between them, often several ΔE on bright papers.
Keep for matching in Convert saves the names and Lab values of the open file, in the measurement condition you picked, in this browser. Convert's Find nearest can then search that library: give it a CMYK value and a printing profile, or any color, and it lists your library's closest colors by ΔE00.
This is how to work with a licensed library you own, such as a PANTONE CxF export: the file stays with you, and huebic never stores or sends it.
Where the file has both a spectrum and the instrument's Lab, the list shows the difference between the file's Lab and huebic's own calculation under the same light and observer. It should be close to 0; a large number means the file's Lab was made a different way, or under another light than it says.
Screens can't show every printed color: a white dot on a swatch means the color is outside sRGB and is shown as the nearest one a screen can. Open in Convert takes the exact Lab, so its CMYK card converts it through your printing profile without that detour.