The potentially (currently) untameable ones, with examples of each, are:
- SilithidScarabSkinBlack: (steel grey with tan markings) Qiraji Scarab
- SilithidScarabSkinGold: (copper with blue markings) Gold Beetle
- SilithidScarabSkinTan: (tan with brown markings) Silithid Searcher from Thousand Needles (possibly extinct)
- SilithidScarabSkinWhite: (white with black markings) Spitting Scarab
- SilithidScarabSkinYellow: (gold with blue markings) Gorishi Tunneler
- SilithidScarabSkinGreen: (green with purple markings). Not seen in game, but found on wowmodelviewer
- UldumScarabSkinTeal: (blue/teal with green spots) Turquoise Scarab (new skin in Cataclysm)
The most worrying one is SilithidScarabSkinTan, which seems to have ONLY ever been used on beetles in silithid hives in Thousand Needles. I think they all drowned. If you're going past the area, please remember to add a suggestion to add a few back amongst the aqua silithids there

Also, as I mentioned before, UldumScarabSkinTeal was the only Uldum scarab skin I didn't notice on Temple Scarabs. But I may have been unlucky. Has anyone seen it? If so, could you please post a screenshot? Note that it looks quite similar to the "blue" skin, but the two small spots on the back are green instead of blue.