I render background grid and enable show shillhouette of mesh on the background grid but i want to change color to black.How can I do that I cant find in Tools->Options.Shillhouette on background grid
I'm sorry to have to say that you can't do that without changing the code. I have find a workaround that may or may not be valid for you.
Start from your current configuration, enabling "Render->Background Grid" and "Show Shilhouette", which will be rendered in white color.
Select option "File->Save Snapshot" and choose the option "Background: Solid Black" before of click con "Save button"
Disable "Render->Background Grid" and take another snapshot, this time with "Transparent backgroud"
Open the grid image with an image editor (photoshop, gimp, imagemagick, etc...) and Invert Colors in the image. You will get something like this:
If this shilhouette is what you expected... congratulations. Dont worry about the surface mesh being inverted.