simple steps to increase user experience for 10% population

http://colorfilter.wickline.org/
http://www.vischeck.com/vischeck/vischeckImage.php
http://www.vischeck.com/vischeck/vischeckURL.php

Different studies have produced different results,
but it is estimated that between 10-12% of people have some form of color blindness.
Using these simple website tools you can increase the usability of your sites and associated graphics!

I hope this is helpful and profitable.

Also:

1. test your sites at different resolutions
2. Test in the JAWS screen reader
4. Use skiplinks and the accesskey attribute
5. use semantic markup (proper heading tag usage)
6. Proper use of alt tags to describe images
7.test how your site functions with javascript disabled
8. make sure to use the label tag properly in forms and provide a legend
9. Never use a font under 12px (i prefer using em but thats your choice) and be sure the zoom function doesn't break your layout
10. Check the WCAG 2.0 guidelines against your site

I also recommend finding an accessibility forum and joining it.

Dear "calm",
thanks so much for your 3 links.

Although I design websites since 93, I never knew ofthis.
I went and checked 2 of my sites, and have to say that I was pleasant surprised. Ergo, my instincts were leading me right.

But I bookmarked your linksnow and will use it from now on.
What a great service. This should be on any web designers list on top.