When I build a site I tend to do a bit of graphic design (developer style) in Paint.NET, but how do I know the colors will all display properly on all browsers on different machines? What color depth to you generally code for? 16bit 256 colors etc.
I shamelessly steal lots of color styles from here. I haven't had much trouble with the color schemes on most peoples' computers.
I say this noting that I'm not a web designer, but a programmer who is forced to design webpages on occasion, so take that for what it's worth.
related or possible duplicate of http://stackoverflow.com/questions/199378/best-css-color-wheel-sites
I don't worry about whether the colors will display perfectly everywhere, as even the most basic of cell phones support 16-bit color.
In my opinion, the days of having to worry about 'web-safe' colors is mostly over.
As long as you're not using colors incredibly similar to each other, you should be good.
According to w3schools only 2% of visitors still have 256-color displays. If you don't use web colors, they'll just see somewhat different colors from what you intended, so there's not really any reason to stick to web-safe colors, which really limit your choices.
On a related note: be aware of using png's.
Different image editors (not sure about Paint.NET) embed the so called gamma correction information in the png. This gamma correction info is used by some browsers and makes the png look different than the rgb colors that you expect.
I have personally encountered this problem on several projects where a png transition to a background color was a perfect match in firefox but not in IE.
Best practice is to remove the gamma correction using pngcrush. Which is a good idea anyway since it reduces overall filesize, even when gamma correction is not an issue at hand.
Here's some more info if you fancy some reading: http://hsivonen.iki.fi/png-gamma
Sorry if this sounds kindof offtopic but I just thought I'd mention it to you when using colors and Paint.NET for use on the web.