Transparency

I was in a doctor's office when I saw large pieces of artwork on the wall. The work was abstract and used transparency - the effect was pretty striking. I don't know if I'll necessarily use this element for my own project, but I really enjoyed the aesthetic. According to this article:
http://gdbasics.com/index.php?s=transparency
transparency suggests clarity and directness.
Here's an example of transparency in business cards:

I don't like the entire card being transparent, but I like transparency in colors and the faded, transparent effect.