Color Deficiency
About 8% of men and 0.04% of women suffer from some form of color deficiency.
Where Has the Color Blue Gone?
The older people get, the more difficult it becomes to tell the difference between one shade of blue and another. Small blue text becomes increasingly difficult to read, to the point that the text becomes unreadable. Therefore, don't select blue as your site's text color.
Having said that, don't change the convention of blue underlined links. Web users have the option of setting their own text and hyperlinks colors in their browser. Make sure you don't override user preferences for text and link colors, which many Web designers mistakenly do.
Bright Blue and Red Headache
Looking at bright blue and red together can cause a headache-inducing condition called Chromostereopsis. This condition causes the viewer to perceive that one color floating above the other. So, avoid using bright red and blue on the same Web page