WowAce

The colors on all of my bars are darker than they should be.

In the screenshot you can see five WeakAuras squares colored in the exact same color as the SUF standard shaman class color. However in the target health bar, which uses class colors as well, it is significantly darker.

I doublechecked this using a Color Picker on the screenshots made of the UI. The little color squares in the SUF color options menu, which serve as a preview of the color chosen, display the correct, lighter color... yet on the target health bar it is darker. I tried changing setting for the target frame around, including other bar textures etc.
It is the same on all other frames as well: all colors appear darker than what they are set to be in the options menu. The squares in the SUF color options menu show the correct one, it's only on the bars that they are darker.

What is causing this?

Things like bar texture or alpha will make colors appear darker or different from what is set.

SUF is setting the correct colors, and any visual differences are due to the above.