A scanner does not see color. It turns the picture into shades of gray and decides, square by square, whether each one is dark or light. Every color rule for QR codes comes from that one fact.
Rule 1: measure the brightness gap, not the hue
The number that matters is the contrast ratio, the same one web designers use for text. Black on white is 21 to 1. The contrast checker calculates it for any pair.
| Ratio | Verdict |
|---|---|
| 7 to 1 or more | Excellent. Scans in poor light, on gloss, on old phones |
| 4.5 to 7 | Good for print and screens |
| 3 to 4.5 | Marginal. Expect failures in dim rooms |
| Under 3 | Do not print it |
Do this
Deep purple modules (#4B3FBF) on cream (#FFF8EE). Ratio about 8 to 1.
Not this
Coral modules (#FF7F50) on white. Ratio 2.5 to 1. Looks lively, fails in a café at night.
Rule 2: dark modules, light background
The specification assumes dark squares on a light background. Modern phone cameras, including every iPhone, will also read the inverse, but many dedicated scanners, older Android apps and some point-of-sale devices will not. If the code will only ever be scanned by phones you control, an inverted code is a choice. On a public poster it is a gamble. The inverted codes guide covers the exceptions.
Do this
A black code on a white tile placed on the dark brand background.
Not this
White modules straight onto the dark brand background, so the whole poster is one inverted code.
Rule 3: brand colors go on the modules, if they are dark enough
Most brand palettes have one color that passes: the navy, the forest green, the deep red. Use that for the modules and keep the background white or near-white. If every brand color is light, keep the code black and use the brand color for a frame or a tile behind it.
Do this
Modules in the brand's dark teal (#0B5C5A), white background, brand orange in the frame text.
Not this
Modules in the brand orange (#F5A623) because it is the primary color. Ratio 2 to 1.
Rule 4: gradients and patterns are fine until they are not
A gradient from navy to black is fine. A gradient from navy to sky blue fails where it goes light. Photographic fills fail wherever the photo has a light patch. Test the lightest point.
Common mistake
Approving the code on a bright screen. Screens add contrast. Print it and look at it under the light where it will live.
Rule 5: paper and lighting eat contrast
Glossy paper reflects the room. Colored paper tints the background. Dim light and shadows narrow the gap further. Every one of these takes a chunk of your ratio, so start with more than you think you need.
Try it in QR Studio
QR Studio shows the contrast ratio as you pick colors and blocks export below 3 to 1 unless you confirm you know what you are doing.
Checklist
- Contrast ratio of 4.5 to 1 or better, checked with the tool
- Dark modules on a light background, or a deliberate and tested exception
- Gradient’s lightest stop checked on its own
- Tested printed, on the final paper, in the final lighting
- Scannability tester run on the exported artwork
Try it yourself
Enter your brand colors and see the ratio, the verdict, and a live code you can scan with your phone.