The shallow version, which you should skip
Walking in alone, photographing people's front doors, and leaving. The Bo-Kaap isn't a film set; the brightly painted houses are people's homes. Selfie tourism has worn out its welcome, and you'll feel it.
The version worth doing
A guided food walk or cook-along. The kind where you go into a home, learn bobotie and koeksisters from the person who cooks them, and eat lunch. That's the Bo-Kaap worth having: a culture, not a backdrop. The community benefits; you get the food the way it's actually made. Book one. It costs less than a fancy dinner and it's the meal you'll remember.
The history in brief
The Bo-Kaap is the oldest surviving Cape Malay neighbourhood, built by enslaved and freed people from Southeast Asia, the Indian Ocean, and the Cape. The pastel houses are recent; the culture, the cooking, the calls to prayer from the Auwal Mosque, the klopse carnival, is centuries old. A guide explains what you're looking at, which is more than the paint.
When to go
Morning, when the light is soft, the calls to prayer are audible, and the streets are quiet. Avoid the tour-bus hour around ten. And don't come only for the photos. Come for lunch and stay for the history.
A note on the photos
The coloured houses are why most people come, and they're worth seeing. But the residents have asked, repeatedly and publicly, for visitors not to photograph them in their doorways and windows. If you take a photo, frame the street, not the person. The cook-along is the better reason to be here, and it's the one that gives you a relationship to the place instead of a picture of it.