My printed colors look different from the screen.

This is expected, and it catches every first-time author. Screens emit light in RGB, so colors look bright and saturated. Print is ink on paper (CMYK), which reflects light and can't reproduce the most glowing screen colors — so prints tend to look slightly darker, warmer, and less vivid than your monitor.

What to do:

• Order a physical proof before publishing — it's the only reliable way to judge real printed color. See Do I still need to order a physical proof copy?
• Avoid ultra-bright neons and pure blues for critical elements; they shift most in print.
• Expect deep blacks and dark backgrounds to look a touch different on cream vs white paper.

None of this means your file is wrong — it's the nature of screen vs. print. A proof takes the guesswork out.