1. Will they sound darker than my high beams?
Yes, the Lo-Riders are slightly darker than the Hi Beams as they are a bit more mid-focused with less top end.
Another option for you would be the Sunbeams, which are basically the nickel-plated version of the Hi Beams. They would give you a smoother top end with less clank and a mellower, warmer bottom.
2. Will they raise my action because they are higher tension? ARE they higher tension or is it just that they're less flexible?
Every time you change the type/gauges of strings, you should always do a complete setup.
That said, when I tried the Sunbeams and the Lo-Riders back to back last year, I only had to do a minor truss rod tweak, maybe a quarter turn. One thing to keep in mind is "tension" (overall pulling weight exerted on the neck) is not the same as "stiffness/flexibility". When we talk about the hex-core strings being "stiffer", that doesn't mean they're harder on the neck necessarily.