It’s so easy when using colour to get carried away and use every colour to make a bright and attractive design or interface. Don’t forget however that not all of us see colour in the same way. Accessibility for all user including those with colour blindness, dyslexia (who find certain colours helpful when try to read) and other sight issues should always be the basis of a good design. If the visually challenged are to appreciate and successfully utilise your design then most others users should be able too. The BBC have a great set of guidelines and it’s worth investigating others standard providers such as the Web Accessibility Initiative If you have a friend or client that has any issues makes sure you include them in any user testing. They will appreciate the time and effort you put into accommodating their requirements and you’ll end up with design that can be viewed by all.