There is a known "emboldening" effect on text when transparency is added to a page. Is that what you mean by blurry?
It will help, but not cure, to be sure all text is above any transparency in the stacking order.
Okay, thanks, yeah black text get an "emboldening effect" but white text seem to get a thinner outline somehow... Is it supposed to be like that?
The stacking order doesn't seem to have an impact I'm afraid.
Basically, there's nothing you can do about the effect on screen or in low-res printing. It generally doesn't show in press output.