Possible to suck color from sprites?

[ItsMeAlan]

I know this might be an unusual request, but in my game I would like for the entire world (that is, all sprites) to become monochrome, except for a few select sprites. Is there a simple way to do this with 2dtoolkit? If not, is there a complex way?

[LaserDinosaur]

There's two ways I know of.

1) Full screen shaders, which apparently are a Pro only feature.
2) Apply a material shader to the sprite. I found a pretty good shader on the forums which I applied to my sprites. I found turning down the saturation rather than messing about with the colour channels gave a much better grayscale look.

Note that if you go option #2, you'll need to create a second material in tk2d, otherwise it will apply to all your sprites in the sprite collection. I'm rather new to tk2d myself, so there might be a better way of that.