Why not apply consistent colours to the letters of e-books and in word processors to allow people with difficulty spelling or reading to recognise words by the colour pattern? Interesting links at the bottom.
Synaesthesia is a mixing of the senses; numbers and letters have colours, smells have sounds, and so on. There is a great synaesthesia generator which you can play with to get the idea, but as with most properties of the mind, I suspect we all have it a bit. More info on wikipedia. [I think I have a form of it called Number Form relating to times and dates - my weeks have a shape that fits into the shape of my year. Audible words also have faint visual echoes of their written shape.]
Learning to read and spell
It is well known that when we read, we learn first to recognise individual letters. Slowly, we get used to common words, and as our vocabulary expands and we read more, we stop looking at individual letters and start recognising whole words.
Those who read a lot get used to seeing the right shape for a given word, so when they come to spell it themselves, they can immediately see whether the word 'looks right'. For example, if I write hospital as hosptial, you can still guess the right word, but you know it is wrong.
Some people have more difficulty reading or spelling, either from reading less or due to learning difficulties like dyslexia. It's entirely understandable - mass reading is a very recent (and fairly unnatural) behaviour which the brain is inevitably going to have difficulty with.
The Original Idea
Could we make use of synaesthesia to provide additional visual cues to the mind? If we added consistent colours to the letters, would that allow us to add more mechanisms to support the response that a word doesn't look right?
One page on the net quotes the statistic that 15% of synaesthetes have a close family member with dyslexia, which suggests some commonality in the mechanisms of the two.
In a blog post, a syneasthete wondered about this topic in May 07. From a recent comment:
"My daughter, aged 11 is dyslexic and has grapheme-colour synesthesia. The colors negatively affect her ability to read and to spell, since some of the letters have the same color. E and U are both green, for example. She also tends to group the colors and hence inserts letters into words because she thinks their colors “go together”." - Mary G.
These would suggest that adding colours to the letters would make things worse rather than better, as there is more going on. In fact, one site considers ADHD a form of sensory overload, and of a sample of people with learning difficulties found 25% of synaesthetes to have ADHD.
So this may well limit usage of the letter colouring to non-synaesthetes