As far as my knowledge of reptilian shape shifting goes, there are multiple modalities by which it is achieved by various reptilian races.

One is by actual shape-shifting, meaning that the individual can (at-will or by another means) change form into a reptile. As far as I understand, this actually occurs very infrequently and is certainly not the norm by any means. I am not sure how this is even possible, but I imagine it is some sort of advanced from of "Chameleon camouflage".

Another, method is by use of Holographic imagery as you spoke about, Blue Metal. This is more common and is advanced enough technologically speaking as to be completely indistinguishable from an actual human and can for all intents and purposes disguise a reptilian being indefinitely.

Another means is when HUMAN individuals happen to possess such a high concentration of reptilian DNA that they can at times actually appear reptilian. Usually aided by extreme emotions that originate in the reptilian brain.

The other one that I have heard about is a species of reptilian that uses cybernetic tech to grow human flesh over their reptilian body as to appear human. This may have been done AEons ago during wars that occurred between reptilians and humans in other star systems. The reptilians, in an attempt to infiltrate the human society, (or Pleiedian or Lyran society more accurately) disguised themselves using this technology.

I have heard reports of Blonde/Blue/White tall Nordic looking beings with reptilian eyes with the vertical slits. I believe this was the race from Aldebaran that aided the Nazis.

I have also heard of instances where the reptilians will eat humans in an effort to consume the hormones which aid in maintaining the human form. When this is done, they apparently prefer children who have not hit puberty yet. After a human hits puberty, and again after their first coitus experience, the hormones in the human body change. This apparently negates the desired effect or severely diminishes the ability to maintain a human form when consumed by a reptilian.

That is the information I have gathered. How much of it is true or not I cannot verify through any personal experience.

So like all information in this field- take it all in with a grain of salt. Just as long as you take it all in.