Make text semi-transparent, but give it a solid outline.
Generally the solid outline will make sure that the text is readable, and the semi-transparent text will let the background through. This is useful if you want to avoid the issue of poor readability but still make the text more visually interesting.
If the text is too transparent the background might still distract from the reading experience. Also text outlines are tricky because they interfere with all of the hard work the type designer has done in the first place.
