most men have more trouble distinguishing colors on the comparator block than women do. Don't know the reason but it's been documented. I have also read that with practice that men can learn to differentiate between the slight shade differences on the comparator, especially if they have a woman look at the block also and compare notes, so to speak. I know this isn't much help but you might want to test with the FAS-DPD for TC which will give you a definite endpoint so there is no question and then with OTO so you can learn what the results are supposed to look like.