Perceptual sensitivity to smooth changes in global illumination over time will depend on the temporal response properties of underlying neuronal mechanisms. Chromatic adaptation, a major contributory factor to color constancy, for example, will set limits on the perceptibility of illumination changes. If adaptation were instantaneous and perfect, even fast changes in illumination may remain below threshold perceptibility. Although there are instantaneous mechanisms that contribute to color constancy (
Barbur, 2004), it is generally accepted that chromatic adaptation is a multiphase process, taking place on multiple time scales at multiple levels in the human visual system (
Rinner & Gegenfurtner, 2000;
Werner, 2014). The time course of chromatic adaptation is also typically measured as the time for color appearance to stabilize after an abrupt change, rather than the phase lag in following smooth changes. A recent study (
Spieringhs, Murdoch, & Vogels, 2019) directly compared adaptation progression following abrupt versus smooth changes, and found distinct time constants for the two. After abrupt changes, although most compensation occurs within the first minute of illumination swap (
Fairchild & Lennie, 1992;
Fairchild & Reniff, 1995) it might take up to 5 minutes to reach full stabilization of color appearance (
Gupta et al., 2020;
Hunt, 1950;
Jameson, Hurvich, & Varner, 1979). More generally, the temporal response properties of chromatic and luminance neuronal mechanisms are characterized by temporal contrast sensitivity functions, with a particular focus on the critical fusion frequency (CFF), or the upper limit at which periodic temporal changes may be followed. In general, CFFs are higher for luminance versus chromatic modulations (
Swanson et al., 1987), and vary across individual cone mechanisms as well as higher-order neuronal mechanisms (parvocellular versus magnocellular;
Huchzermeyer & Kremers, 2016;
Huchzermeyer & Kremers, 2017;
Huchzermeyer et al., 2018); CFFs also vary with mean retinal illuminance and stimulus size. It is important to note nonvisual neuronal mechanisms might also influence behavioral responses to temporal changes in illumination. For example, neurons in the suprachiasmatic nucleus of mice are shown to respond to temporal changes in the chromaticity of daylight (
Walmsley et al., 2015). Whether such responses exist in the human nonvisual neural pathways and interact with the visual responses is an open question. Here, we focus on the lower limit of perceptibility of aperiodic temporal changes in chromaticity, for large-field, constant luminance stimuli.