One of the most common issues we run into making websites accessible is contrast -- making sure the difference between the color and brightness of the text against the background is enough that it's clearly readable.
Blue text on a dark background can be very difficult to read -- but it's not just brightness. Red-green color-blindness affects around 8% of males around the world. Take a screen out into bright sunlight and try to read text that's similar brightness to its background, and you can start to understand that contrast issues affect everyone.