The detector hands you three codes for every color, and they're the same color — #2563EB, rgb(37, 99, 235) and hsl(217, 84%, 53%) describe identical light. The reason all three survive is that each is good at a job the others are bad at.
Six hexadecimal digits, two per channel — that's rgb in base 16, compressed for transport. Nobody reads #2563EB and pictures a blue, and that's fine: HEX isn't for reading, it's for moving. It pastes into CSS, Figma, Slack, and paint-store websites without ceremony, and it survives being said over the phone. When in doubt, hand off HEX.
The same three numbers in honest decimal. The moment your color needs math — transparency via rgba(), a gradient midpoint, pixel data from a canvas — you want channels you can do arithmetic on. It's also the raw form this site's engine actually reads from your camera: everything else is derived.
Hue (the angle on the color wheel, 0–360), saturation (gray to vivid), lightness (black to white). It's the only notation matching how people talk: "same blue, a bit darker" is just lightness minus ten, hue untouched. Building a palette of one hue at five lightnesses, or nudging a text color until it passes contrast without changing its character — that's HSL territory, and it's exactly how our checker computes its fix suggestion.
CMYK — the ink-percentages notation for print. Screens and printers make color by opposite methods (adding light versus subtracting it with ink), and the conversion depends on the specific printer, paper and ink profile. Any website converting HEX to CMYK without asking which press is guessing politely. If your color is going to print, the honest route is: HEX to your print shop, let their profile do the conversion.
So: read it with the detector, hand off the HEX, compute with RGB, adjust in HSL. Three costumes, one color, no mysticism required.