Our palette is small on purpose. Black leads and appears most; White, Gray and Smoke support it. Use the colors in the proportions shown here, and take values from the tiles rather than sampling them from screen.
Black carries most of the weight across a piece. White gives room to breathe, while Gray and Smoke support and accent it. Keep Black as the lead color in every layout.
Contrast matters most here: text has to stay clear and legible. Use Black text on White or Smoke backgrounds, and White text on Black. Gray is best kept for secondary details, and avoid low-contrast mixes.
Use the color values the guide lists for each medium. Screen work uses the RGB and web values, while print work uses the CMYK or Pantone values listed in the tiles. Check printed proofs against the screen, since the two can look different.