The easiest way is to buy cheap disposable foam brushes and use one for each color, then throw them out. They are usually under a dollar. Or you can get chip brushes that use bristles, but a very cheap and do the same.

I like the mini foam rollers that come with a tray. Rinse and wring the roller out well because it makes loading with paint better/easier. Can do several colors with one roller but if you're doing colors of white most of them are going to need 3 coats to reach full color opacity. Both on the sample and on the walls. So, it'd be faster to have a roller per color.

You can wash and re-use a brush, and paint when it's still wet.

I appreciate it, y’all! Thanks.

Or use Samplize- that’s what I’ve moved to. You can then shift the paint samples around to view them next to certain design elements in the room/look at them in direct and indirect light. Much cleaner and more useful than painting your walls directly.