What's My JND?
Hard Mode

Nine squares. One is a different colour. Find it.

The gap between squares means no gradient to help you - just raw colour perception. It takes about 40 rounds. Your JND will likely be higher than easy mode. That's the point.

Let's go What is this? Read the post. Or try the easy mode.

ΔE_OK

Your ΔE_OK JND
Hard Mode

Either you have superhuman cone cells or you got very lucky. I'm going with lucky. This is absurdly below the theoretical JND. Your monitor is doing something weird. Or both. This shouldn't be possible. I'm not saying you cheated, but not not saying that. Okay, either you're a mantis shrimp in a trenchcoat or your display has a secret wide-gamut mode nobody told me about. Suspiciously impressive. Okay this is genuinely impressive. You're well below the standard JND of 0.02. The CIE should be sending you a job offer. Or at least a certificate. You're seeing differences that most colour scientists would call noise. If you're not already calibrating displays for a living, you're leaving money on the table. Genuinely remarkable. You sailed past the theoretical human limit like it owed you money. I'd accuse you of cheating but I don't actually know how you'd cheat at this. Very nice. Comfortably below the 0.02 JND that the colour science people say is the limit. You'd make an excellent paint-chip inspector. Is that a job? It should be. Better than most. You can see differences that half the population would swear don't exist. Your opinions about colour palettes are now legally binding. Solidly below the standard JND. You probably get unreasonably annoyed when someone says two slightly different blues are 'the same colour'. You're right, by the way. They're wrong. Right around the 0.02 JND, which is where most humans land. The CIE would be proud. You are a perfectly calibrated observer. Well done being average, I guess. Textbook human vision. The colour science papers were written about people exactly like you. That's a compliment. Probably. You've landed smack on the theoretical JND for human vision. Statistically normal. Perceptually unremarkable. I mean that in the nicest possible way. Slightly above the standard JND. Not bad! Most people who actually try end up here. You can tell colours apart when it matters, and you're not wasting your life squinting at imperceptible differences. Honestly that's a win. A bit above the standard JND, but honestly, the differences you missed were genuinely tiny. You're well within 'normal human' territory. Whatever that means. Look, the colours you couldn't tell apart? Neither could most people. You've got better things to do than split hairs over sub-perceptual colour differences. Hard mode is hard. The gaps between squares strip away the gradient hint your brain relies on. This is a respectable score given the format. Without the gradient transition to lean on, your brain is doing pure colour comparison. This is a tougher test than it looks. You did fine. The gap between squares is doing a lot of heavy lifting against you here. Your eyes are working harder than they would in easy mode. Hard mode is genuinely hard. The gaps remove the gradient transition that normally helps your brain. Display calibration, ambient lighting, and screen brightness all matter even more here. This format is brutal. Without adjacent colour comparison your brain has to rely on memory across a gap. Try the easy mode first if you haven't. Rough. But in your defence, the gap between squares makes this dramatically harder than it looks. Environment matters even more here. Try a dark room. Read the post about this. Try the easy mode.