# QR code colours not scanning

> Decoders convert the image to greyscale before deciding dark from light, so what matters is luminance difference, not how different the colours look. Two visually distinct colours can have nearly identical luminance and produce a code no scanner reads.

Source: https://useqr.app/docs/troubleshooting/qr-code-colors-not-scanning · Last reviewed 2026-08-21 · UseQR is free forever, MIT licensed, no signup.

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## Luminance, not hue

A mid-tone red on a mid-tone green looks strongly contrasting to a human and is nearly
identical in luminance. After greyscale conversion the decoder sees two similar greys and
cannot place a threshold.

Relative luminance weights green heavily, red moderately and blue very little:

```
L = 0.2126·R + 0.7152·G + 0.0722·B   (on linearised channels)
```

That is why **dark blue on black** fails badly (blue contributes almost nothing) and why
**yellow modules** almost never work (yellow is very bright).

## Working thresholds

| Luminance difference | Result |
|---|---|
| Above 60% | Reliable in most conditions |
| 40–60% | Works in good light; marginal in dim rooms |
| 30–40% | Fails on many cameras |
| Below 30% | Effectively unreadable |

Measured on screen these are best case. Printing, laminating, dim lighting and an angled
camera all reduce effective contrast, so leave headroom.

## Rules that hold

1. **Dark modules, light background.** Inverted codes are supported inconsistently.
2. **Never yellow, light green, cyan or pale orange for the modules.** All are too bright.
3. **Avoid dark blue on black** and other low-luminance pairs that look contrasting.
4. **Gradients must keep the darkest and lightest points within the contrast rule**, not just
   the average.
5. **Photographic backgrounds** almost never work, because contrast varies across the code.

## The safe way to use brand colour

Use the brand colour for the **modules**, on a **white** background — that maximises the
luminance difference while keeping the code recognisably yours. Colouring the background
instead is where most branded codes fail.

If the brand colour is too light, use a darkened variant for the code. A slightly darker
brand blue that scans everywhere is better than the exact swatch that does not.

## Check, do not guess

Our [validator](/validate) computes the real luminance contrast of your chosen pair and
decodes the rendered output, so you get a number rather than an opinion.

## FAQ

### Why does my colourful QR code not scan even though the colours look very different?
Decoders work on luminance after greyscale conversion. Colours that contrast strongly in hue can have almost identical luminance, leaving the decoder no threshold to work with.

### Can I use my brand colour in a QR code?
Usually, if you apply it to the modules and keep the background white. If the brand colour is light, use a darkened variant. Colouring the background is where most branded codes fail.

### Why do yellow QR codes never work?
Yellow has very high relative luminance, so yellow modules are barely darker than a white background. There is no threshold for the decoder to find.

### Can I invert a QR code — light modules on a dark background?
Some scanners handle it, many do not. There is no functional benefit, so it is a gamble taken for aesthetics alone.

## Try it

- https://useqr.app/validate
- https://useqr.app/url