What exactly is the difference between "Grayscale" and "RGBA" font anti-aliasing settings?

I've just switched to Ubuntu, and I'm trying to replicate the Windows ClearType font quality using the Unity Tweak Tool. The default anti-aliasing is "Grayscale", and I'm trying to change it to "RGBA", however, I'm not seeing any perceptible difference. Is it a problem with the tweak tool, with Unity, or something else?

Solution 1:

According to similar questions on Ubuntu's support community, the "Grayscale" option is standard grayscale antialiasing whereas the "RGBA" option is subpixel antialiasing for LCD screens.

To see a difference between the two, you can temporarily increase the scaling to something huge and try each option. The larger font scale should allow you to see any differences in font edges.

Also, not sure why it defaults to grayscale. Based on questions at http://help.ubuntu.com it appears that most applications seem to prefer either the "RGBA" or "None" settings.