To study which hues are associated with brief excitations of foveal middle-wavelength (M) cones, two highly practiced color-normal observers (the authors) gave basic color names to 500 and 530 nm increments. The test spots were presented to the fovea and foveola in conditions that included M-cone isolation. 1 degrees and 3.6 min arc tests were flashed for 200 ms on steady 8.6', 1 degrees, or 10 degrees mono-chromatic adapting fields (481, 530, 610, and 630 nm), or on mixtures of these fields, or on a dark field. Tests were flashed at 1, 2, 4, and 8 x thresholds. Field hue had little overall effect. Yellow, green, blue-green, and blue color-names were elicited, both for the foveal 1 degrees tests and for 3.6 min tests confined to the S-cone free foveola. These data add to previous research by showing a contribution of M-cones to blueness on monochromatic fields, as well as on achromatic fields. Because the 500 and 530 nm tests appear green when presented steadily on these same fields, the M-cone contribution to blue may well be transitory. (C) 2001 John Wiley & Sons, Inc.