Crystal was the colorless version of the Character plugs, Airwindows ‘Virtual Console Collection’ years before anyone else was doing it. The idea was, make a ‘colorless’ version with all the same functionality, so people could try it out.
The Character plugins grew into BussColors, which let you switch between them and is still around and popular. Back in the day, though, you picked between plugins like ‘Luxor’, ‘Neverland’ and ‘APIcolypse’. The plugins dynamically generated convolution impulses based on the signal coming in, which is true even of the ‘colorless’ Crystal: its convolution impulse is simply a filter for the highest supersonic frequencies, with no added color or character.
The Character plugins (and Crystal) also had a saturation effect briefly seen in Channel, where the output was flat up until you hit a certain point and then switched to a gradual saturation curve. You can shift between very gradual saturation or hard clipping or anything in between. Thing is, I learned that way that people don’t like discontinuities in the transfer function: this feature didn’t sound as good to people as a single smooth curve.
But you can experiment with it for free with Crystal. Crystal’s also got an interesting trick on its output stage: it’s applying a ditherlike noise, but rather than applying it as a value it’s applying a blend between the output sample and the previous output sample. This makes high frequency content soften and fuzz, without adding noise to low frequency stuff or to silence. It’s there in Crystal, subtly, so if that sounds interesting give it a try.