Use the same guidelines for or your interior doors. If you like the idea of statement door knobs and hinges, go for lots of contrast— dark door knobs and hinges on light doors, for example. As an aside, interior door levers, which you simply have to push down, are easier for aging hands to operate as compared to door knobs, which you have to twist.
Let’s talk first about metals. As a general rule, I like to keep the different metals in a kitchen to no more than two. If you have stainless steel appliances, that counts as one metal. So that leaves one other metal you can bring into a kitchen. If you’ve got brass light fixtures, that’s your one other metal. Your new hardware should be nickel or brass.