1.3.3 Sensory characteristics
The guideline says:
Instructions provided for understanding and operating content do not rely solely on sensory characteristics of components such as shape, colour, size, visual location, orientation, or sound.
What does that mean?
What do I need to do?
This could be misinterpreted as an instruction to avoid the use of colour, shape, position and so on... but all it really is, is a reminder that you need more. You can have an arrow at the bottom of the page for your next button, but just make sure it is labelled in such a way that a screen reader can read it. It may need alt text, for example.
I think one of the worst offenders in this category is schools. Schools use all kinds of documents, forms and spreadsheets that rely on colour coding. To be fair, many teachers mark books using colour coding. Colour is so important to us.
We used to use red, orange and green spots on risk assessments. We colour coded progress spreadsheets, using red, yellow, green and blue to indicate whether each child had not progressed, progressed less than they should, progressed as they should or progressed further than they should. I use the phrase, 'as they should' partially in jest, of course. Who says they should?!!
I quite like to use icons when I'm designing user interfaces, especially for my eLearning. However, icons rely on visual perception, so I always either give them alt text, or better still, use a combination of icon and words. For example, my next button might be a box containing a right arrow and the word NEXT. My previous button would be a left arrow and the word PREV. It just means people don't have to rely on sight.
A lot of this comes down to thought and awareness. It's about getting into the habit of thinking from another person's perspective. If I now said, "Click on the red circle on the left to see some examples of bad practice," you would have to be able to see colour, shape and position, to find where to click. You would also have to be able to use a mouse, most likely. That's a lot of assumed abilities, considering my possible audience. I could consider adding text into my red circle that a screen reader could pick up. That way, the whole red circle representing bad practice thing is still there but I haven't excluded anyone. I would also need to change the instruction so that it didn't rely on sight. Something like, "Click on the BAD PRACTICE button that follows this paragraph, to see some examples of bad practice."
Just for the record, there is no button... it was just an example!