The PDF is in full colour on screen. The printer has colour cartridges. You hit print — and out comes a black-and-white version of your beautifully designed document.
Nine times out of ten, this is a driver setting silently forcing greyscale. Sometimes it's the file itself. Let's check both.
What's actually going wrong
Greyscale forced in print dialog. Print drivers often default to 'Print in greyscale (black and white)' to save toner. Printer-side setting. Some printers have a physical switch or menu setting overriding the driver. PDF is grayscale. The file itself was exported in grayscale colour space, so even sent to a colour printer, only black ink fires. Low colour cartridge. Some printers fall back to black when colour ink is low.
Check the print dialog first. The 'Color' or 'Print in greyscale' checkbox is the most common culprit.
The quick fix
Open the print dialog. Find the section labelled Color, Output, or Quality. Uncheck 'Print in greyscale' or set output to 'Color' explicitly. Print again. For most users, that's it.
If the option is missing or the print still comes out monochrome, check your printer's menu — many have a setting that overrides the driver. Reset to 'Auto' or 'Color'.
If that didn't work
The PDF might actually be greyscale. Open it and look at any colour element — does it appear desaturated even on screen? If yes, the file has no colour to print.
Convert to Word, check colour rendering in Word, then re-export with the colour profile set correctly. Or, if you have the source document, re-export from there with 'High quality' or 'Print' export settings — those preserve colour, where 'Standard' sometimes converts to grayscale.
Check colour cartridge levels. A printer with empty cyan will print magenta-yellow approximations of colour and may fall back to black entirely on some drivers.
Prevent it next time
Set your printer's default profile to colour rather than greyscale if you print mostly colour. When exporting from design apps, choose a print-quality preset. And keep an eye on cartridge levels — partial colour cartridges are unpredictable.
FAQ
Why does my colour printer print PDFs in black and white?
Almost certainly a 'print in greyscale' setting in your driver or printer menu. Uncheck it. The setting is often on by default to save toner in office environments.
Can a PDF be greyscale even if it looks colour?
It can have a colour preview but be stored in greyscale colour space — rare, but it happens with some export workflows. Convert via Flint and re-export from the source app to fix.
Why is my colour washed out when printed?
Colour profile mismatch. The PDF is sRGB but the printer expects CMYK. Most home printers handle this fine, but design-grade output needs colour profiles set correctly at export.
Will my photos print better as a PDF or as images?
Same quality if the PDF embeds full-resolution images. For pure photo prints, print as JPG directly. For mixed documents with photos, PDF is fine.
Most colour-print failures are a single checkbox. If it's the file itself, convert via Flint and re-export from source with print quality on.