Thirty artists' colors have been exposed for 12 weeks to 120ppb of formaldehyde in purified air as well as to purified air alone (control experiment). The exposure was carried out in the dark at ambient temperature (19±2°C) and humidity (RH44- 52per thousand). Color change (DELTAE) was measured using a reflectance color analyzer after one, two, three, four, six, eight, 11 and 12 weeks of exposure. Color parameters (x, y, X, Y, Z, L^*, a^*, b^* and DELTAE) were also calculated from the 380-700nm spectra, recorded with a reflectance spectrophotometer, of unexposed colorants and of colorants exposed for 12 weeks to purified air and to formaldehyde. Regression analysis of the two data sets indicated that the color changes measured by these two methods were in excellent agreement (near- unity slopes, with correlation coefficients greater than 0.99). Exposure to either formaldehyde or pure air on water-color paper resulted in little or no color change for all the colorants tested, including inorganic colorants, alizarin lakes, quinacridones, triphenyl methanes, indigo derivatives, arylamides and natural colorants such as curcumin. Formaldehyde, which is ubiquitous in indoor air, including museum air, does not appear to be a major threat to colorants in museum collections.