What you are seeing
This fix finds which stage changed the colours and restores a pair that prints with strong contrast. You will compare the proof with the design, check the printer and the stock, and reprint a single corrected proof. Fall back to black on white if a colour pair will not print reliably.
Likely causes
1.
Screen colours do not match print colours — Quick test: compare a printed proof with the screen design under good light.
2.
Wrong colour profile or mode — Quick test: check the file colour settings and the printer profile.
3.
Stock changes the colour — Quick test: print the same file on plain white stock and compare.
4.
Low ink or toner — Quick test: print a test page and check for missing or faint colours.
5.
Colour pair too close in lightness — Quick test: view a photo of the code in greyscale and check the contrast.
Step-by-step fix
Step 1: Print one proof on the real stock and compare it with the screen design under good light.
Step 2: Photograph the proof and view it in greyscale. If the modules blur together, contrast is the problem.
Step 3: Check the file colour settings and the printer profile for a mismatch.
Step 4: Print the same file on plain white stock. If it improves, the stock is shifting the colour.
Step 5: Strengthen the pair: darken the modules, lighten the background, and increase the lightness difference.
Step 6: Check the ink or toner level and print a test page if a colour looks faint or missing.
Step 7: Reprint one corrected proof and confirm it scans on two phones. Fall back to black on white if the colour pair still fails.
Putting this into practice
In practice, keep one approved colour pair per stock, proven by a printed proof. A pair that prints well on white coated stock may fail on kraft or recycled stock, and the proof is what tells you. Record the before-and-after behaviour with the job file, so the fix is provable rather than anecdotal. When the same failure appears again, that record tells you whether the old fix held or a new cause appeared.
Common mistakes to avoid
- Approving a colour pair from a screen preview without ever printing a proof on the real stock.
- Reprinting the full run before a single proof passes, which turns one failure into many.
- Testing on one phone in ideal conditions instead of two phones in the real conditions where a code that prints with wrong colours will be used.
- Changing the artwork and the placement at the same time, so you cannot tell which change fixed a code that prints with wrong colours.- Skipping the proof test because the change looked small, when small changes cause most repeat failures.
Quick checklist
- The printed colours match the design on the real stock
- Greyscale contrast is strong on the printed proof
- The proof scans on two phones
- The corrected proof passes on two phones in the real conditions
- The fix is recorded in the job file so the next reprint starts from a proven setup
- Every printed copy is checked against the approved proof
- The proof is retested after any later change to the link, design, or placement
Related tools and guides
- [QR minimum size checker](/qr-minimum-size-checker)
- [QR contrast checker](/qr-contrast-checker)
- [QR print proof checklist](/qr-print-proof-checklist)
- [QR DPI calculator](/qr-dpi-calculator)
- [QR quiet zone calculator](/qr-quiet-zone-calculator)
- [printed QR tester](/printed-qr-tester)
- [QR size calculator](/qr-size-calculator)
