So, I couldn't leave well enough alone. I was also too burned out on work to make progress, so I went back and revisited the N throbber, using the simpler technique (shrink at RGB, then index colors), and also added an alpha channel. I think it looks a lot better.
But I couldn't stop there -- I did what I probably should have done first -- I made a throbbing "F" for Firefox in the style of the N throbber. See yesterday's post for instructions to install it.
