Type in a hex color code to search for it in the chosen palette.
It will tell you the chances of it being selected for random generation.
If it's 0%, that means that exact color code does not exist in the palette.
waitwut?
"Why can't I find my color here?"
Hex color codes allow for 16,777,216 colors, but Mabinogi's palettes only contain 65,536 entries (with many of them being duplicated colors). That means that ~99.6% of random color codes you may want don't actually exist in any given dye palette in Mabinogi.
"Then how come I've seen dyes of (x color) before?"
Dyes generated by gachapons and events often have their color codes typed manually by the devs into the reward script, so they're not actually randomly-generated and thus not subject to the limited palette... but as a result are much less available. If you're dead-set on that #E711CF color that came out of a gacha/event way back, you just have to hope they decide to stick that color in future things.
"Then how come Dyelite finds it in the minigame?"
The colors this tool checks against are the game's true palette colors. Screenshots of dye palettes taken in-game will often be slightly off, generally due to video driver color correction and monitor color profiles. Thus Dyelite might be reading slightly different colors than will actually be applied. Usually the resulting difference is minor enough to not be noticed, however.
Dyelite doesn't just search for your color code, it will search for and "find" colors that are close to yours as well, in the same way that this tool will suggest similar colors that actually do exist in the palette.
"What does '12 points off' mean?"
If you have Dyelite's error slider set at 25 (for example), it'll find colors up to 25 points away from your entered code. The similar colors that this tool suggests uses the same type of comparison as Dyelite, it's simply how "close" the color code is, with bigger numbers being further away.