Both cameras are
big upgrades over the K100D! With the K-x, you will lose the red focus lights in the viewfinder, but you'll still have the green hexagon to tell you that it's grabbed focus.
Do you feel like you've outgrown the K100D's controls, or are you still happy with it? The K-x will have a similar number of external controls (though several more functions are easily available, like ISO, WB, etc.) The K-7 will give you many more controls, including a front dial under your index finger. The K-7 also is weathersealed, has a larger and higher resolution LCD screen, bigger and brighter viewfinder, built-in level, and can do 30fps videos. (And lots of other upgrades.) The K-x, on the other hand, is notably smaller and lighter and has better high ISO performance (at least a full stop better, I'd say.)
Oh, and the K-x comes in all those pretty colors. Basic black only for the K-7.