The original colours for the Triceratops badnik were available on ICEknight's site, in the original Digitizer art for them. I don't know where these pictures are still available, but I do know that they didn't correspond with the first pallette line (Sonic / Tails's pallette).
However, the original art for them as pictured in the Digitizer art and found in previous prototypes actually appears green using the second pallette line in HPZ (Leftover GHZ pallette line, changed to accommodate Sonic 2 rings), and doesn't appear correctly using Sonic's pallette.
The ones in your picture, on the other hand appear differently, and do indeed appear to have been redrawn to use Sonic's pallette as the other badniks in the Zone do - interesting, since it suggests that they were still considering developing Hidden Palace further at one point and adding these badniks into the Zone.
More confirmation that their art has been redrawn; the sprites found in previous prototypes used a cross-hatch dithering style on the grey area around the 'bot's horns. This dithering has been redrawn into a smooth gradient in this version.
Looks like this enemy wasn't abandoned as early in development as initially thought. Excellent find, Neo! = )
This post has been edited by McAleeCh: 24 February 2008 - 03:34 PM