There are only three differences we can ascertain; one is obviously the lighting. The K68 has red LEDs only, whereas the K68 RGB offers RGB lighting. The K68 RGB is also available with either Cherry MX Red or Blue switches (the K68 has only the MX Red option), and it costs $20 more.
It’s worth noting, though, that these two keyboards are part of a new group of Corsair keyboards that have a slightly different design language than the reigning crop. This group includes the growing K63 family (K63, K63 Wireless, Wireless Special Edition, and wireless-plus-lapboard combo).
The most obvious difference is that the K68 and K63 keyboards don’t have the brushed metal top plate of most of the rest of Corsair’s keyboard family. Instead, they have a colored backplate with a top panel that covers just enough of it that you get a certain type of underglow. There are also somewhat subtle differences in the rear “fin” of the keyboards and the look of the front bezel and wrist rest attachment.
All of the above factor into price; it seems that with the K68 and K63 series, Corsair is budgetizing a bit while offering a key feature or two that you don’t get on its other keyboards. For example, the K68 planks have IP32 waterproofing, and all but one of the K63 models have wireless capabilities.
In terms of price, the K68 RGB is $120, the K68 is $100, and the two K63 wireless models are $110. (The wireless K63 and lapboard combo costs $160.) The non-wireless K63 is just $80, which is the least expensive mechanical Corsair keyboard you can get.
It’s true that various iterations of the K70 family cost between $120-$130, which puts them on par or close to price parity with some of the K68 and K63 models, but note that none of them have RGB. And as you can see with the K68 RGB versus K68 pricing, RGB is a $20 markup. Most of the rest of Corsair’s mechanical keyboards run between $130-200.
In other words, Corsair is letting its flagship K95 series sit pat for now while it fleshes out options in the middle of its product stack. It seems the peripherals giant is looking for new angles to attract new customers.