My mom is allergic to scented products (thanks to me
she was fine before she got pregnant with me) so we've always used the hypo-allergenic detergents. Usually Purex. My clothes never smelled of anything after washing (unless they'd been left wet in the washer a few days.) I've switched to scented detergent, because I'm not allergic and I like having the mild scent because psychologically it feels cleaner.
But the point is that the dyes and scents aren't going to make a difference in the actual performance of the detergent. The scent is cosmetic.
ETA: I'm so helpful, aren't I? "No, that's not the reason!" but not offering any suggestions of my own.
I hope you figure it out soon!