How to use AIS_Triangulation?

Dear all:

I know AIS_Shape is more convenient. But some big files are not necessary to load the Topo data. So I try to load STL file just for visualization. For this goal, I hit plateaus.

First, I can't add ComputeSelection to AIS_Triangulation, because there are no topos. How to add ComputeSelection for AIS_Triangulation?

Second, Some colors are not work. For example, Quantity_NOC_BLACK is fine. But Quantity_NOC_GRAY is not work, the displayed color is similary with Brass.

Finally, the displayed model is odd, maybe it caused by there is no WireFrame.

Thanks for replys, I would glad to get some advices.

Here are the codes

 Handle(Poly_Triangulation) aSTLMesh = RWStl::ReadFile(theFileNmae.c_str());
Handle(AIS_Triangulation) tris = new AIS_Triangulation(aSTLMesh);
int numNodes = aSTLMesh->NbNodes();
Quantity_Color color;
int RGB_I;
color.Color2argb(Quantity_NOC_GRAY, RGB_I);
Handle(TColStd_HArray1OfInteger) colors = new TColStd_HArray1OfInteger(1, numNodes);
for (int i = 1; i <= numNodes; ++i) 
{
    colors->SetValue(i, RGB_I);
}
tris->SetColors(colors);

Handle(Prs3d_Drawer) theDrawer = new Prs3d_Drawer();
Handle(Prs3d_LineAspect) theLineAspect = new Prs3d_LineAspect(Quantity_NOC_BLACK, Aspect_TOL_SOLID, 1.0);
theDrawer->SetFaceBoundaryAspect(theLineAspect);
tris->SetAttributes(theDrawer);
//tris->SetDisplayMode(Graphic3d_TypeOfShadingModel_PhongFacet);