Sequential schemes are suited to ordered data that progress from low to high. Lightness steps dominate the look of these schemes, with light colors for low data values to dark colors for high data values.
Divergent schemes put equal emphasis on mid-range critical values and extremes at both ends of the data range. The critical value or break in the middle of the gradient is emphasized with light colors and low and high extremes are emphasized with dark colors that have contrasting hues.
Qualitative schemes do not imply magnitude differences between data ranges, and hues are used to create the primary visual differences between gradient colors. Qualitative schemes are best suited to representing nominal or categorical data.
A few color schemes commonly used for scientific visualization applications that deviate from these definitions (e.g. RdBlGr, a divergent scheme with black as the mid-range color) are also included.
See http://colorbrewer.org for further details.