Sometimes a limited palette of colors can actually seem more colorful than a full spectrum of rainbow colors. As a case in point, consider these two compositions, limited to a specific cast of irises and tulips, so essentially two strong colors (with, of course, variations within each color).

Each of the two colors vibrates against the other, and one is swept away in the tidal pool of complementary colors, but with a limited palette. 

Every color can be suggested in a black and white composition. Similarly, when moving away from monochromatic, less can sometimes be more. So consider limiting your colors when selecting your color palette for a chromatic composition!