The Use of Filters and Transparency Layers in Website Design | Daily Magazine | Scoop.it
It seems that with one trend in website design, designers almost have another trend pushed upon them. This is the case with large background images – using a slide show with a variety of different photographs means that whatever color text you choose it will show up better on some than on others, so the solution has been to place a filter or transparent layer between the image and the text, meaning that the text will show just as clearly on any image.

Via Jakarta Web Developer