User blog comment:DaNASCAT/Technical Update: December 11, 2012/@comment-3441771-20121212034223/@comment-188432-20121212175604

In my experience, I've never enjoyed the opacity:whatever effect. I think — and maybe it's just my eyes playing tricks with me — that it makes the text less clear. I prefer to add a repeating background image which has a 70% opacity, which is a slightly different thing to having the CSS directly control the opacity. Another advantage to this method is that you can have the background to be transparent, but of any colour. So you can get transparent #fff white or transparent #b0b0b0 grey-white or what have you. Using just opacity:whatever gives you considerably less precision than, in effect, adding a coloured gel in front of your transparency effect.