I'm not colour blind. I'm not even green blind. And I'm definitely not red/green blind.
If you're thinking about colour impairments, please keep this in mind: just because some people have a colour impairment that doesn't mean they are all colour blind (most of them aren't). They can see just what you can see, but some parts of the spectrum may appear paler and thus the nuances may be hard to tell apart. They'll probably have little problem telling two colours apart when they touch, but can't reliably recognise them as distinct when they're not.
It's okay to use colour in your design. It's even okay to use colours that are often problematic for people with colour impairments. It's not okay to RELY on them, tho. Especially if you rely on telling roughly similar colours apart (say, bluish purple and blue, or even dark red and dark green).
If you have to use colour as a signal, use another one as a failsafe -- use different patterns, borders or underlines in addition to different-coloured fills, outlines and texts.
The idea is not to sacrifice, but to enhance -- this is true for every form of accessibility, actually.
If you can't use strongly contrasting colours (i.e. different hue and value at high saturation) due to design constraints, simply make sure colour is not the only contrast you provide -- if all else fails just use markup to ensure the unstyled page still retains a contrast.
Oh, and don't forget to set your background and text colours in pairs. Even if you want to keep the default for one of them (white background, black text). This is not for accessibility alone, this is also for people like me who use a dark desktop theme and curse every time they see a form with black text on a (desktop default) dark background or a white background with (desktop default) bright green text on it. Like this very form I'm writing in -- good thing the web developer toolbar comes with a "ignore page colours" option.