This is going to depend on the installer. Its the same thing as asking an installer to run a mirror to another TV in a home that is pre-wired. If its not on the work order, they don't get paid to do it, and the installer generally won't do it.
As a national sales partner for Dish who wrote thousands of work orders for new installs, we could never promise the customer something beyond the work order even for something as simple as hooking up a DVD player. When the extra work was promised, it never got done and we then had the customer screaming at us on the phone after the technician left.
You can always ask, just be prepared to tip him when he is done.
I used to run the extra cables off the Dish to the ground block when I was a technician because customers where always thinking of adding other receivers and I wanted to make the job easier when I came back. When very few customers would call me back, I figured I should save the money and time and run only 1 cable.
As far as running the extra cable, you just use tie straps to attatch the extra cables coming down the house from the Dish and you will be ok.
To ansewer the cable issue. The installers generally carry black cable, and on occasion they will have a roll of white cable. The only other color you can easily get is a cream colored cable that looks almost like its pink.
Grey, cream, and blue cable and generally hard to get and needs to be special ordered.
