The color of the slider can be changed using the following using CSS, and we can dinamically change it, when the change event is triggered, using jQuery like this:
I have prepared a sample in the Kendo UI Dojo that demonstrates this approach; you can take a look at it here
Regarding your second question, there is no support for changing the width of our Kendo UI Slider; I encourage you to participate in the Kendo UI Feedback and Feature Request Portal
and, if enough people vote on your request, developers might include it in future releases of Kendo UI Professional.
I hope this helps!
Telerik by Progress