Where appropriate, software should support different device formats. For example, websites should be designed to work on screens of all sizes.
Contrast should be high enough between elements that are supposed to be perceived as different elements. A person should be able to tell them apart.
Any text should be easy to read.
Information should have redundancy. For example, any image should come with alt text which explains what the image shows, for those people who cannot see the image.
Software uses signifiers to let a person know what they can interact with. There should be plenty of these.
That said, the visual design of the interface should never obscure the interaction design. For example, flashy colours and animations should not mean that a person cannot tell what they can or should interact with.
A person should constantly be aware of the status of the software they’re using.
Software should also guide a person’s vision well, so they get a sense of where they should look next.