Top and bottom: Mammillaria plumosa(s), Center: Austrocylindropuntia vestita cristata
Taking care of these is a bit different from their green counterpart as they are donned with a wonderful coat of soft, feathery spines which protects them from the scorching heat of the sun by deflecting light and also allows them to transpire less. As a result, they require less watering and can handle full sun better. Keep them away from humid areas and if possible, avoid wetting their "tomentum" as these can be stained in the long run. Same is applicable with non-cacti succulents with heavy farina (powdery coating). Happy Gardening and Happy Weekend!