Here's a tricky one for you! ...at least, for me.
I'm working on creating my own font with the handy-dandy SpriteFont object (thank you, 
Ashley!). Given that my game focuses on a contrast between dark and soft, glowing lighted areas, I wanted my font to reflect that, too. This is namely for the HUD information, as well.
If you look in the Examples folder that comes with C2, you'll see a capx for Lighting, where simple manipulation of the blending effect turns a fading circle into a flashlight. Keep that in mind...
Back to the Spritefont. Picture a solid block on the screen - all one color. Everything around and behind it is black, dark. But bring that flashlight object around behind it, and suddenly you see the outline - a silhouette, if you will - of letters and numbers. Portions of the block are actually transparent - the alpha level of the color reduced - whereas the letters, of course, are fully solid. Just like in those suspense movies where the guy gets kidnapped and comes to with a bright light in his face and some mystery man standing between him and the light. All you can make out is the man's shape, but his face is darkened because the light is behind him. That's almost exactly the effect I'm going for. But before the light is ON, I need to figure out how to blend two colors to LOOK like "one".
For instance, if I have an RGB setting of green (alpha: 255), what would the RGB setting have to be in order to produce a nearly identical color as before but with a reduced alpha level? They LOOK alike at a glance, but with the flashlight, they'll CLEARLY be different.
I'm hoping the artists among us will have a ready answer, but if you have any input, please feel free to suggest an option. I'm willing to try anything. THANK YOU!