As for Glamdring glowing blue, I haven't come across any references in The LOTR--yet. The following is from The Hobbit, "Over Hill and Under Hill":
"Bright as blue flame," however, may only be a reference to the brightness of the sword, not its colour. Mind you, when Frodo is upon the flet in Lothlorien while Orcs are prowling about below, Sting is described as flashing and glittering "like a blue flame."Then Gandalf lit up his wand. Of course it was Gandalf,; but just then they were too busy to ask how he got there. He took out his sword again, and again it flashed in the dark by itself. It burned with a rage that made it gleam if goblins were about; now it was bright as blue flame for delight in the killing of the great lord of the cave.
Hopefully someone will find a passage in the Lord of the Rings that clears this up--but I suspect that you have stumbled upon a Tolkien myth. Perhaps the idea that Glamdring glows blue when orcs are near is a misconception.