I've recently been learning a lot about the L*a*b (or Lab) color space, for image manipulation.
To see why, here's a simple experiment you can do: Open up an image in Photoshop and convert it from RGB mode to Lab Color mode. Add a Curves effect layer (or just edit the curve) and tweak the a and b channels. Choke them down so that a 90% input equals a 100% output, and a 10% input equals a 0% output.
Now compare the original image to the tweak. You can't do this by simply turning up the saturation, either...
Norman Koren walks you through the basics.
A while back, I got ahold of a Tamron CF Tele-Macro 80-210mm f/3.8-4. It was my first experience with a Tamron Adaptall-2 lens.
I like the lens. The bokeh's a little harsh, but it's very sharp, built like a tank, and can focus down to just under a meter. However: It came with a plain-Jane Pentax K adaptor.