Ideas: 1). You could do a combination of wood and black details on the island. ( See Photo # 1) Try to contact the original cabinet company that who made the existing cabinets, you would be assured the wood color will match. They may offer a black cabinet paint or stain to achieve this look. 2). If you can't find the cabinet company, Sherwin Williams is excellent source to match up wood stains, just take them a piece of unfinished oak wood and one of your doors. Try to match up the stain color as close as you can to your existing oak stain cabinets. If not quite perfect match, than add a black glaze over top.

No, I mean--seriously? Only you can make that decision; "dark sage" means nothing concrete. It could be any of dozens in a range of colors and lightness/darkness. Go to the hardware store, buy one brown, one black cover plate and see which one you like. Problem solved. $2. It's so simple. You could be done by now.

HI -- Your kitchen is very nice but it is all dark finishes . You could visit a cabinet shop and look at their lighter finishes and perhaps get some gables ( finished wood panels ) and put those on . But I am not sure that is going to brighten up the kitchen alone . Maybe see if you can add some L.E.D. pot lights If you meant brighten with some color then add some decor items or have bar stools in a color . I do think a lighter finish on the island matching a color to the countertop would look nice .

Pictures are always advisable when you want specific recommendations because the best choice colors depend on on many elements within a space. If you are using Cambria Weybourne counters and Repose gray on the walls then SW Dovetail 7018 or Guantlet 7019 should offer the contrast you are looking for without being too harsh. Good luck.