Printful Says Converting to CMYK Lowers Accuracy. Gelato Says Pre-Converted CMYK Is the Most Accurate.

That sounds like fence-sitting until you read the pages. Six print services publish colour advice for the files they print, and they give three incompatible recipes. Printful says converting to CMYK before you upload lowers accuracy. Gelato’s poster page says a pre-converted CMYK file gives the most accurate colour. Redbubble says design in CMYK and then convert to RGB before uploading, which is exactly the file Printful warns about.

Worse, the two services that name a specific CMYK do not name the same one. One is a 2004 American sheetfed offset condition, the other a 2013 European one, and their ink limits differ by ten points. A third names only a “Generic CMYK Profile”. So “send CMYK” is not an instruction, it is a category.

None of them is wrong. They are describing different presses, and on posters the press changes with the size of the print in centimetres.

Which Colour Mode Does Each Service Ask For?

Every line below is quoted from the service’s own help page. The page date matters, so it is in the table.

One caution on those dates. Printful’s and Mixbook’s timestamps are bulk-save stamps, when a batch of articles was re-saved, not the day the advice changed. Treat them as “no later than”, not “as of”.

Where Do Printful and Gelato Say Opposite Things?

Word for word, because the overlap is exact.

Printful:

Converting your files to CMYK before uploading can unnecessarily reduce the available color information and lead to less accurate results.

And on the same page, “we don’t recommend using CMYK files as the final upload format for Printful”.

Gelato, on its poster page:

For the most accurate color reproduction, provide files in pre-converted CMYK PDF/X4 format with a “GRACoL2006_Coated1v2.icc” output intent.

Both sentences are about accuracy, on posters, for a file you are about to upload. They point in opposite directions.

The reason is in Printful’s own explanation: “Some of our printing techniques use additional inks beyond the traditional CMYK set to reproduce a wider range of colors.” If the press has more than four inks, handing it a four-ink file throws away colour the press could have printed. Gelato’s poster page is describing a workflow where the conversion is going to happen anyway, and it would rather you controlled it than left it to its software.

Note also what Gelato’s own formats page says, which is not the same as its poster page: “For vibrant and colorful posters, canvas prints, apparel, mugs, acrylic, and metallic products, use sRGB image files.” The poster page optimises for accurate, the formats page for vibrant. Those are different goals and they get different answers from the same company.

What Is Redbubble’s Recipe, and Why Is It the File Printful Warns About?

Redbubble publishes the detour explicitly:

For the best of both worlds, you should design your work in the CMYK color profile and convert the finished work into the RGB color profile before uploading.

A file that has been through CMYK and back into RGB has already lost the colours CMYK could not hold. Converting back does not restore them. That is the outcome Printful describes as reduced colour information, arriving by a different route.

Redbubble also closes off Gelato’s answer entirely. Its format rule is “only the following file types are accepted: JPEG and PNG”, and it states that “TIFF and PDF files won’t work correctly”. There is no PDF/X-4 route, so you cannot follow Gelato’s advice on Redbubble even if you wanted to.

On a second Redbubble page the recommendation is stronger still: “We highly recommend designing in CMYK since that is the color profile the third-party printers use.”

Which CMYK Do They Mean?

This is the part that makes the disagreement more than a matter of taste. Both services that name a CMYK condition link or name a registered ICC profile, and the ICC Profile Registry publishes what each one is.

Two different standards, nine years apart, from two different continents, with a ten-point difference in how much ink they allow on the paper. A file built to one is not a file built to the other. Redbubble, meanwhile, names no registered profile at all, only a “Generic CMYK Profile” in its proofing instructions, and Prodigi publishes a separate proofing profile for each paper it prints on while asking you not to embed any of them.

Neither registry entry describes the presses these companies actually run. Both describe offset printing. Posters at this end of the market are printed digitally. The registry says as much about its own limits: “The ICC is unable to recommend profiles for particular applications.”

And sRGB is not one thing either. The ICC’s own sRGB page warns that “The sRGB v4 profile will in some cases not produce the same results as would be obtained using an sRGB v2 profile”. The exact profile Printful names, sRGB IEC61966-2.1, is not listed on that page under that name.

Does the Size of the Poster Change the Press?

On Gelato, yes, and the thresholds are published in centimetres.

Gelato’s own words for the middle band: posters there “may be produced using either digital or inkjet technology, depending on the equipment available at your local production hub”. And for the top band it says the Canon technology “can reproduce a larger color gamut compared to digital printing”.

Read that twice if you sell a size range. The same file, the same service, the same colour settings, printed on two different machines with two different gamuts, decided by whether your poster is above or below 50 x 70 cm. Gelato publishes B2 as “50 x 70 cm / 20 x 28 inches”; the centimetre figure is the one its own threshold is written in. A3 as 29.7 x 42 cm comes from IKEA’s paper-size table, which also lists it as 11.7 x 16.5 inches.

So a 40 x 50 cm print sits in the band where Gelato itself cannot tell you which press you will get.

What Happens to Neon Colours?

Same problem, three remedies, and this is the clearest case where following the wrong page gives you the wrong file.

Gelato’s PDF page: “For fluorescent (neon) colors, it is better to use CMYK, as normal sRGB will not come out as expected.” Its poster page then says that on all three of its poster papers, neon and out-of-gamut colours “are converted to CMYK” by Gelato anyway.

Printful’s remedy is the opposite. Neon colours “often don’t have exact printable equivalents, so they may print duller or darker than they appear on screen”, and the fix it gives is to “Preview them with a proof setup and adjust them manually”, staying in sRGB.

Printify does not offer a remedy, it offers a warning: upload CMYK and “our system will convert it to RGB, and the colors might shift significantly”.

How Much Ink Is Too Much?

Four numbers, from two companies, worth knowing if you build dark files.

Gelato adds that if you are happy with how the dark areas look, “you can safely ignore this warning”. A warning you may ignore is a hint, not a limit, and it sits ten points above the ink limit of the very profile Gelato asks you to target.

What Should You Actually Do?

For buyers of printable files, five minutes of care:

1. Keep one master in sRGB and do not convert it.
2. Export a copy per service, following that service’s page rather than general advice.
3. Use a CMYK soft proof to look, never to deliver, unless the service asks for a CMYK PDF by name.
4. If you are ordering above or below 50 x 70 cm on the same design, expect a visible difference and order one of each before you commit to a batch.
5. If you are buying a file from a seller, ask which colour profile it carries. A seller who knows will answer in one line.

For the related question of why a print looks duller than your screen even when the file is right, our colour management guide covers letting exactly one piece of software manage colour. For the same kind of disagreement about file edges rather than colour, see three vendors and three bleed numbers.

And check the date on any page that tells you what to do with a print file, including this one. Every quotation above was read on 12 October 2026.

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