Color Mode while Painting?

[Viridis]

Okay guys, here's the thing. I've been painting in Photoshop on and off for about...five years, maybe a little more. This semester I signed up for a class in Digital Rendering and am taking it as an independent study, mainly because I need the extra credits for electives.

Generally I'm being given leeway to paint what I want, but I'm really having some trouble working within the parameters the teacher is telling me to do, because they seem to conflict with the established "system" I've figured out over the years.

The first issue came up this afternoon, as I tried to work on one of my assignments. The teacher is insisting that I paint in CMYK because we're meant to act as if we're working for print. All well and good, but my colors look like absolute rubbish in CMYK, and I can't get any darks at all, just pathetic washed-out greys.

So my question is, for those of you who paint work regularly in Photoshop, are you painting entirely while in CMYK? Or are you working in RGB (which is after all how a screen works) and then converting it over to CMYK once it's done and ready for print? And if you work in CMYK, how the hell do you get proper blacks/dark colors to show up? I really want to work on this, but I can't get anything done if I don't know what colors I'm even using. :/

Any comments here will be helpful.

[Metsys]

I always work in RGB mode. The reason why is that working in CMYK mode is considerably slower than RGB mode, some filters won't work the way you expect them too or at all, and the file size is larger.

When I'm doing stuff for print I'll use a CMYK-safe palette to pick my colors (I have them available at http://glenmoyes.blogspot.com/2008/10/color-wheel-photoshop-swatches.html and http://glenmoyes.blogspot.com/2009/01/color-wheel-swatches-shades.html), and then convert the file to CMYK when I'm done while still keeping the RGB copy. Occasionally I'll turn on the gammut warning to check to see which colors are out of gammut. If there's a few splotches it's no big deal, but if there's a large area then I'll go look into it, but usually that doesn't happen if I'm using my CMYK-safe swatches and avoid using some of the blend modes.

About the dark colors not showing up, I've never experienced that problem. I'd need to see a screen shot and some more details about how you work to figure that out. My only guess right now is that you may have a weird color profile set for CMYK mode, but if you left it as the default that shouldn't be the problem.

[Viridis]

Yeah, I did some Googling and got basically the same answer. It seems most people work in RGB and then just convert a copy of the file over to CMYK for printing.

From what I found, the reason my darks were going weird was because I was using shades very close to black, and that.. causes some kind of problem in CMYK because it's a subtractive mode or something something something. I did find out it was a fairly common issue-- and yes, all settings are on the default.

What I find strange is my teacher's insistence on working in CMYK. Not only do a lot of brushes/filters apparently not work well in CMYK, you get bigger file sizes too. So I'm not sure why he would advise this. But then, he's also suggested I use the blur/smudge tool to soften some things in my work, which is... almost as bad as using the lens flare, at least from what I was taught.

Anyway, it seems I have my answer (ignore the teacher's advice and just paint in RGB), so thanks for your input. :3

EDIT: Although, now I'm curious-- what is this "gammut warning" stuff you're talking about? How would I check that?

[Metsys]

It's under View > Gamut Warning (Shift+Ctrl+Y).

When working in RGB you can turn that view mode on and any pixels with colors that cannot be printed faithfully because of the limitations of the CMYK pigments will be marked as gray. It's warning you that those colors will change when printed.

This is actually part of the reason why I've been looking into hexachrome printing; CMYK sucks.