[Muzman]

Like some folk here, I'm sure, I have neither the money nor the time (or in my case, the inclination) to go to the shopping centre with pen and paper for hours or splash out on brushes and paint.
There has been some mention before of what good practice it is to work with traditional limitations; gauche is the most common example mentioned.
Fred said once that using index colour in photoshop might be good for simulating some aspects of gauche. I'd say it's too limited colour wise, and the way it handles edges is too harsh (maybe I'm doing it wrong).
How about this: Paintbrush set to 100% opacity with pressure affecting size (size box ticked); pick your own swatch; no undos.

How's that sound?
Folk needn't worry about the "nothing beats the real thing" line. This isn't about beating it; PS won't simulate real light, media build up, brush feel etc. It's about translating what makes it good practice to the computer. I'm basing this on what some have said (spooge for one) about certain kinds of painting forcing you to reduce the amount of mistakes you can make.
But I've never used them so I don't know.
So, if anyone has ideas on how this can be implimented in photoshop in a small way, tell us all.

[Trance-R]

Mmm...
I think setting the airbrush to multiply would help.. yeah... but why don't you just use MetaCreation's Painter Classic? It simulates traditional media much better. And the palette knife is much uh.. faster and realistic.
Have a good one.

[Fred Flick Stone]

The only way I use photoshop is with the opacity checked, and the color opacity set to 100%. If you do this and create a few custom brushes, it should, to a certain degree, feel like working with watercolor.

If you want to try this for limiting your pallette, go to your color picker, and set up a custom pallette using the pantone colors, and grab a traditional pallette, by refering to a how to paint book, and try painting a picture using just those few colors selected, plus the settings I mentioned above. Now, lets say you pick Primary red, primary yellow, and primary blue as your pallette, you can go into te color picker and adjust the value slider to darken, and deepen the color your using. I hope that helps a bit, as I really don't methodically paint with photoshop. I just fly by the seat of my pants...