OK :)

I managed how to achieve what I want.

I discovered that (it seems) the problems is that after calling:

moi.view.surfaceColorMode = "FixedColor";
moi.view.edgeColorMode = "FixedColor";

the current active viewport (in my case the "3D" viewport) doesn't do a "refresh", so the objects still looks like before.

But, instead, if I other two lines of code, all works as excpeted:

moi.view.surfaceColorMode = "FixedColor";
moi.view.edgeColorMode = "FixedColor";

// just to FORCE the refresh of the active viewport
moi.geometryDatabase.selectAll();
moi.geometryDatabase.deselectAll();

So, now it works.
Anyway...am I using the correct solution?

Thanks.