Regarding your CSS question - yes, it is possible. However, as it is the same HTML element, the only approach that will work, is that you create a custom image that you will use for background of the track element of the slider - the first half of the image will be green and the second half will be red. The area between the two handles is another HTML element - the selection range element. That is why you can style it separately. I have attached a simple page to demonstrate my idea.
As for your second question - this functionality is not yet available out of the box, but you can achieve this effect with some custom code. Please refer to this online article
for information how to do this.
the Telerik team