how to plot a curve with different color on different part?

Hi,
I have a curve, I want to mark some part of this curve with a different color, how can i do that using excel?

for example, a curve as following, I want to mark the point from (4,4) to (6,6) with a different color.
x y
1 1
2 2
3 3
4 4
5 5
6 6

Thanks,

Mike