CMYK vs RGB
Screens mix light (RGB), presses mix ink (CMYK). Ink cannot reach the glowing colors a monitor can, so print comes back quieter.
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What it is
Screens make color by adding light: red, green, and blue lamps firing at you. Paper makes color by subtracting it: cyan, magenta, yellow, and black ink absorbing part of the white sheet's reflection. Two different physics, two different sets of reachable colors, and the ink set is usually the smaller one without being a neat slice out of the other.
The colors that fall off the cliff are the ones a monitor is best at: electric blues, neon greens, hot oranges, pure saturated reds. They come back from press quieter and slightly grayer, which is normal, not a printer error. It does not all run one way though: ink beats a screen on a few deep cyans and saturated yellows, so soft-proof instead of assuming everything shrinks. Keep a tagged RGB master, ask the printer for their output condition (GRACoL, FOGRA, SWOP, or their own digital press profile), convert the production copy once against that profile, and use a spot color when a brand color absolutely has to be exact. A PDF/X-4 workflow can even carry tagged RGB through to the RIP when the shop asks for it.
Gotcha: converting at the last second is where jobs die. An RGB file auto-converted by the printer's software gets whatever profile they happen to have loaded, and your carefully picked hex turns into someone else's guess. Also, pure black text should be 100% K only, never a four-ink black, or small type prints fuzzy when the plates shift.
Ask AI for it
Convert this artwork for print using the printer-supplied ICC profile and their total ink limit, not a generic default. Keep the tagged RGB master untouched and convert only a production copy, once. Soft-proof against that output condition and report every out-of-gamut color with the source hex, the resulting CMYK build, and how far it shifted. Keep body text and small type at 100% K only, use a rich black build the printer approves for large solid black areas, and hold total ink coverage under the limit they published. If the shop runs a PDF/X-4 workflow that accepts tagged RGB, tell me that instead of converting.