2 problems about coloring

There are 2 problems that I've been working for hours but couldn't get the good result (and sorry for my bad english but I tried to make the question as understandable as possible)

1) I have a circle x^2+(y-1)^2=1 and 2 line y=x, y=-x cut the circle, so I want to color the biggest closed area within those line and curve (from pi/4 to 3pi/4 radian). I tried to use the fill() but all failed.

2) I have 2 3d plot on 1 table and want to color each plot to discriminate them

Ex : x^2 +y^2 and e^x + e^y

I tried to use the set() but only the ezplot for 2d successed, the ezsurf for 3d couldn't. And why couldn't I give a variable for the ezsurf() ?

Ex : a= ezplot => ok

     a= ezsurf => error

I'm very appreciated, thank you very much