Childhood experience is thought to be one of the 'causes' of Synesthesia. For instance people who perceive letters as having colours (a is always red, b is blue), often find that these correspond to the colouring of alphabet fridge magnets or toys they had as children.

COoL!

I have tremendous trouble reading a list of color words on a whiteboard, if each is written in a different color from what the word is. E.g. write blue in black; write yellow in red; write red in blue etc.

Extra points - try to say what the color each word is written in, while looking at them. Maybe even harder.

That's the "Stroop effect"