Each color forms a separate grouping which competes for viewer's attention. Note that colors do have cultural connotations. Note that many color recommendations are geared to the requirements of maximum visibility rather than prolonged viewing. Color aids decision making. Color focuses attention.
Color reveals organization and pattern.
Color speeds search. Color elements grab a reader's attention first before the reader has understood the surrounding information context. Saturation intensity, purity, or chroma. Purity of a color. Relative brilliance or dullness of a color.