What is the best colour scheme to use for a shirt design, CMYK or RGB?
It all depends on what kind of t-shirts are you making. What kind of system are you using to apply your design on the t-shirts?
Most of the printers are CMYK-based, so that's the prefered method of working with files. If you work with RGB - the colours will have to be converted to CMYK at one point or another. So CMYK is the way to go.
I have been working in the garment industry for the last 7 years and there are primarily 4 different types of applications:
** Screenprinting: ** Flat solid colours. I recommend using PMS (Pantone Matching System) to get the best results. Deliver in any vector format (EPS, AI, PDF etc) or a high-quality raster images (JPG, PNG etc). When it comes to raster images, make sure they are at least twice the size of what you want with 300DPI to ensure you get the best results, even the smallest details.
** Digital Printing - Heat Transfer:** CMYK - As most of the printers for Digital Heat Transfer usually work with CMYK (sometimes with the addition of white, silver, gold), it's best to use CMYK. It's also recommended to use PMS colours to achieve the results you want.
** Sublimation ** CMYK, recommended to use with PMS as in the previous types of print.
This is a relatively new way to print onto garments. It produces the best feel as the design is in the fabric, the print dyes the fabric under high temperatures. The print doesn't deteriorate* and it feels good. This method has some limitations as it needs to be printed on white shirts, otherwise, you cannot achieve the full range of colours. Also, you can only sublimate on polyester-based t-shirts (I would say minimum 60-70% polyester - otherwise the results will look washed out).
**DTG - Direct to Garment print: ** print straight onto the garment. I don't have much experience with this method so I can't say much. I believe both RGB and CMYK are good in this case. However, CMYK is always safer as most of the printers usually use this combination. RGB colours are used on screen based devices, not printers.
Please note: the design should be given in Vector files as some of the colours might have to be tweaked the manufacturer to give the desired results.
*** colours might deteriorate if printed on a garment with a low polyester count.
I would think CMYK
The CMYK color model (process color, four color) is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key (black). Although it varies by print house, press operator, press manufacturer, and press run, ink is typically applied in the order of the abbreviation
Sort of by it's definition it seems to be the best for screen printing, but you might want to check with whomever is making the shirt.
There are many different answers to this question. You really need to talk to the printer and find out more about their requirements and the production method best suited for your design.
Depending on what you print shop says, the workflow could be any of the following:
Work in RGB. Deliver pdf in RGB.
In this case you create your design in RGB and use your eyes to choose the colors (whether these colors are "correct" depends on the quality and calibration of your monitor). You export a pdf in RGB and leaves the CMYK converting to the print shop. The printer will ideally try to match the colors, as well as possible.
Work in RGB. Deliver pdf in CMYK.
Like in the first case, you work intuitively in RGB, but when exporting the pdf, you convert the colors to CMYK. Since there are many different CMYK profiles, you need to get the correct one from the print shop. Doing the conversion yourself gives you the benefit of seing the converted file with your own eyes. Many bright colors from the RGB color space are not possible to print using CMYK colors, so you might notice a shift in colors.
Work in CMYK. Deliver pdf in CMYK.
You can also work in CMYK all the way through. This way you are rather "construction" colors than "painting" colors. When choosing a CMYK color you manually choose the percentage of each CMYK ink which in the end will lead to a certain size for the tiny raster dots. This is traditionally the way to work, but you are not at all guaranteed that a CMYK color will look the same on different medias using different production techniques. To get the best possible preview when working this way you should set up your application to use the correct CMYK profile provided by the print shop.
Work in spot color. Deliver pdf in spot colors.
If your shirt is going to be silkscreen printed (and if it fits the design) you would often choose a couple of solid colors for printing instead of CMYK. This saves money, gives a cleaner result (especially if you stick to solid colors with no tints) and the possibility of using brighter colors (and maybe even neon and metallic colors).
Most shirts are being printed using inkjet printers on thermo-transfer foil. Those printers often have a bunch of extra inks like light cyan, light magenta or even orange or violet. The printer always tries to match the source as close as possible.
If you convert your design to CMYK, you're effectively losing gamut: CMYK has a numerical range of 4x100 whereas RGB is 3x256.
Of course you can't reproduce many of the vibrant colors of RGB color space but when using CMYK, you're limiting your possibilities. If you've got a decent calibrated display, the printer is able to "guess" how the colors looked like on your monitor.
UPDATE: My opinion is based on daily business as many customers don't use calibrated monitors and become quite unsatisfied with the result if they start designing/converting to CMYK. If you do have a decent calibrated display, CMYK is the way to go in order to achieve the best match between what you see and what you'll get.