RGB vs CMYK: why colors change in print
RGB (red, green, blue) is additive: screens mix light, and the more of each channel you add the closer you get to white. CMYK (cyan, magenta, yellow, key/black) is subtractive: ink absorbs light, and the more you lay down the darker it gets. A monitor can show saturated colors, especially bright greens, electric blues and neon oranges, that ink on paper or fabric can't reproduce.
When you convert a file for print, those out-of-gamut colors get pulled to the nearest printable color, which is why a logo can look duller on paper than on screen. Converting early and proofing in CMYK avoids surprises on press.
Common RGB to CMYK conversions
Values from the same device-independent formula this converter uses:
| Color | HEX | RGB | CMYK (C, M, Y, K) |
|---|---|---|---|
| Black | #000000 | 0, 0, 0 | 0, 0, 0, 100 |
| White | #FFFFFF | 255, 255, 255 | 0, 0, 0, 0 |
| Red | #FF0000 | 255, 0, 0 | 0, 100, 100, 0 |
| Green | #00FF00 | 0, 255, 0 | 100, 0, 100, 0 |
| Blue | #0000FF | 0, 0, 255 | 100, 100, 0, 0 |
| Navy | #000080 | 0, 0, 128 | 100, 100, 0, 50 |
| Teal | #008080 | 0, 128, 128 | 100, 0, 0, 50 |
| Orange | #FFA500 | 255, 165, 0 | 0, 35, 100, 0 |
| 50% gray | #808080 | 128, 128, 128 | 0, 0, 0, 50 |
How the conversion works
The converter first finds black (K) as 1 minus the brightest RGB channel, then works out how much cyan, magenta and yellow are needed for the remaining color. Going the other way, each RGB channel is 255 × (1 − ink) × (1 − black).
This is the standard mathematical conversion. Professional prepress software goes further and uses ICC color profiles (such as GRACoL or FOGRA) that model a specific press, paper and ink. For a critical brand color, ask your printer which profile they use, or specify a Pantone spot color.
Tips for print-ready color
- For deep, rich black on large areas, printers often use a "rich black" such as 60/40/40/100 instead of plain 100% K. Keep small text at 100% K only so it stays crisp.
- Keep total ink coverage under your printer's limit (often 300% or less) to avoid drying and smudging problems.
- For screen printing and embroidery, match to spot colors or thread colors rather than CMYK process.