IF: I've seen shots of the Mars Shadow vessel being dug up and it shimmered with the same colour as the earth background. It would appear that the Shadow being a "living" ship had a sort of chameleon ability that would make it hard to see, the perfect camouflage.
In the episode were Keffer gets fried the Shadow did not appear on his scanner as anything he could recognise and he just got lucky/unlucky that it phased in, in front of him.
Being a "living" ship may have given it a low EM signature. We can assume that the Shadows therefore have a stealth mode by this nature, but would they need to develop a true cloaking system as they can phase in and out of real space at will. They are too powerful to be bothered by the lesser races seeing them and the other Ancients would likely have some way to detect a cloak. IMHO. Phew...
[ October 23, 2002, 00:54: Message edited by: Nomor ]