Three colour vision tests, the Ishihara test, the City University Test (CUT), and the D-15 test were studied as a function of induced intraocular straylight, using a commercially available light-scattering filter. Thirty young individuals (aged 17-28 years) with no ocular abnormalities and normal colour vision participated in the study. Intraocular straylight was estimated in all individuals using a psychophysical compensation method with the C-Quant straylight meter, with and without the light-scattering filter which caused an increase in intraocular straylight typical of that found for cataract. Under normal viewing conditions all the subjects passed each of the 3 tests with no errors. When viewing the Ishihara test plates through the filter, 10 out of the 30 observers made at least 1 error. Three subjects also made errors on the desaturated CUT test plates, but all subjects still passed the D-15 test with the filter. The errors in the Ishihara test correlated with the amount of intraocular straylight, as measured with the C-Quant. This study indicates that interpretation of the Ishihara test in a clinical environment will be made more difficult in individuals with higher levels of straylight.