These tables list the final process color percentages for cyan, magenta, yellow, and black inks that were used to print the Mapping Census 2000 atlas.

Atlas citation:
Brewer, Cynthia. A., and Trudy A. Suchan, U.S. Census Bureau. 2001. Mapping Census 2000: The Geography of U.S. Diversity, Census Special Report CENSR/01-1. Washington, D.C.: U.S. Government Printing Office.
PDF files online: http://www.census.gov/population/www/cen2000/atlas.html

A word of warning about using these colors in ESRI ArcMap 8.x:
ESRI mapping software uses a different conversion from CMYK to RGB for screen display than illustration software (which is more specific to print design). Colors in the tables below will not look good on screen or projected if you type the CMYK into ArcMap (excessive saturation is often a problem). The colors will look like the colors in the printed atlas after you export Postscript from ArcMap for prepress file preparation and proofing (even though the colors look inept on screen in ArcMap). They may also not look good in intermediate-stage color laser prints. My intention in posting these colors online is specifically to help you go to press with a successful scheme.
If you want to use similar schemes for screen display, try out my ColorBrewer tool for selecting schemes and use the RGB specs listed for each option.
As an alternative, if you want to get the exact look you see here on screen in ArcMap (or in another program that takes only RGB), you should first produce RGB conversions using another program. I would do a screen capture of the scheme you want (or save the legend JPEG), paste into Photoshop, and eye-dropper specs from the legend patches. (If you do them before I do, please send them to me and I'll post them here.)

These tables without graphics (more suitable for printing) are available at: CensusAtlasCMYK_no_jpg.html

Colors also used on “Population Density” map (p. 11); skip color 5 in county list.