For that your need to set your D3DFVF flags right.
Basically, without shaders your CUSTOMVERTEX structure needs to be setup with FVFs in such a manner that the color associated with that vertex gets bypassed.
Check this out for further reference --> http://msdn.microsoft.com/en-us/library/windows/desktop/bb172559(v=vs.85).aspx

It's it! Setting
d3dDevice.VertexFormat = VertexFormat.Position;
is skipping the color and making lines white.

I don't want to trouble you more, but is it possible to make this lines thicker? They are very thin and when i use rotation they are partly absorbed by color triangles:

d3dDevice.SetStreamSource(0, vertices, 0, Marshal.SizeOf(typeof(Vertex)));            d3dDevice.VertexFormat = VertexFormat.Position | VertexFormat.Diffuse;            
d3dDevice.Indices = triangles;            
d3dDevice.DrawIndexedPrimitive(PrimitiveType.TriangleList, 0, 0, totalPointsCount, 0, totalPointsCount / 2);            
d3dDevice.VertexFormat = VertexFormat.Position;          
d3dDevice.Indices = lines;            
d3dDevice.DrawIndexedPrimitive(PrimitiveType.LineList, 0, 0, totalPointsCount, 0, totalPointsCount);

Look at the green side of picture, some lines are missing. They are absorbed

For that your need to set your D3DFVF flags right.

Basically, without shaders your CUSTOMVERTEX structure needs to be setup with FVFs in such a manner that the color associated with that vertex gets bypassed.

Check this out for further reference --> http://msdn.microsoft.com/en-us/library/windows/desktop/bb172559(v=vs.85).aspx

It's it! Setting 

d3dDevice.VertexFormat = VertexFormat.Position;

is skipping the color and making lines white.

I don't want to trouble you more, but is it possible to make this lines thicker? They are very thin and when i use rotation they are partly absorbed by color triangles:

d3dDevice.SetStreamSource(0, vertices, 0, Marshal.SizeOf(typeof(Vertex)));

            d3dDevice.VertexFormat = VertexFormat.Position | VertexFormat.Diffuse;
            d3dDevice.Indices = triangles;
            d3dDevice.DrawIndexedPrimitive(PrimitiveType.TriangleList, 0, 0, totalPointsCount, 0, totalPointsCount / 2);

            d3dDevice.VertexFormat = VertexFormat.Position;
            d3dDevice.Indices = lines;
            d3dDevice.DrawIndexedPrimitive(PrimitiveType.LineList, 0, 0, totalPointsCount, 0, totalPointsCount);

http://imageshack.us/photo/my-images/27/capture4df.png/

Look at the green side of picture, some lines are missing. They are absorbed