Have you ever been in the situation where a mockup introduced a new color, but it's quite similar to the ones you already use? Or you wanted to clean up a colors.scss with $grey-lighter-7 and its cousins?
ClosestColor analyses your existing color palette - which you can add as CSS/SCSS/SASS) files or in the textarea. Afterwards, you can enter the color you want to compare, and we find the closest match.
ClosestColor calculates a color difference (ΔE) according to CIE94. Generally speaking, a difference <2.3 is imperceptible, anything >5 will be seen as different color.