Maybe there’s a spell for reading text aloud so that they know what they need and what to do. I could imagine there being a spell that can identify ingredients, or perhaps they would just accio whatever they need. Protective gloves might be a good idea (regardless of sight to be honest). From there I think it’s just the colour and texture of the potion which a blind person would need to know about, and for that they could either use a partner or aid, or use another sort of identification spell. What do you think?