I have heard of using an egg white tempered with a little very warm soup and then whisked into the main pot and brought to a simmer. The egg white is cooked but in such small pieces it has the effect of lightening the color of the soup. I've never tried it, but this method might be what you're looking for, although I don't know of any specific name for doing this.
"Food is our common ground, a universal experience." - James Beard