Consider the value of a pattern as a background for text according to what you can—or cannot—read below this box.
Notice as well that some colours are unpleasant even if you can see the text clearly.
If you highlight the gap between the red and brown paragraphs, you'll see that some colour combinations can make text quite invisible!
Different text colours look different on differently coloured backgrounds.
Some colours harmonise and look well together if one is light and the other dark.
Busy backgrounds are terrible, no matter what colour the text.
Sometimes two colours seem almost to vibrate at the edges making reading unpleasant.
If colours are too much alike in strength, the text can be impossible to read.
Strong colours against soft backgrounds are easy to read.
A strong colour on an off-white background is easy on the eyes.
How this colour looks depends very much on its background.
This colour may look strong or be hardly visible.