Observers viewed a thin (1.0-1.5 degree) annular mixture of 450 plus 660 nm light with the left eye, and a 4.8 degrees circular 660 nm adapting field with the right eye. The annular test was centered upon the adapting field in the fused percept. The contralateral field, which bleached negligible photopigment, caused the test to appear more reddish; however quantitative results reject the hypothesis that a given contralateral 660 nm light simply adds redness to the test. Additional experiments with a separate 660 nm adapting light presented to each eye reveal that fused chromatic adapting fields affect a complex central mechanism. For example, a dim background presented to the same eye as the annular test can reduce the effect of an opposite-eye field, even when the dim test-eye background has no measurable influence in a purely monocular experiment.