Android :: Seek Bar, - Change Path Color From Yellow To White

I have two questions:

1) how do I change the color of the seek bar (path) from yellow (the default color) to white. What I mean to say is, while I slide the thumb , it turns the line traversed from grey to yellow. I want track/line to either remain grey or white..Basically I want just the thumb to move with no color change in the seek bar.

2)
How to change the thumb of seekbar from rectangle to circle/sphere/round shape.