Two ways
1)
You can change the color of the source (color solid 7 1) but that will change all instances of that object throughout the project.
2)
Alternatively you can use filters to change the color of just the one clone:
-Apply a Threshold filter, and drag both the threshold and smoothness parameters to 0
-Apply a Colorize filter and remap white to the color you want.
Hope that helps
/Anders