These are the vertices of your triangle. You have to zoom in very, very close.
As I already explained here:
https://forums.ldraw.org/thread-27965-po...l#pid52656
"It could happen that your screen gets darker and darker the more you zoom in. Just double-click one of the neighboring triangles of the vertex you are zooming in".
Read also point 6 in:
https://forums.ldraw.org/thread-18260-po...l#pid20717
w.
LEGO ergo sum