What Mars texture is used here?
The texture is exactly the same as the L11 textures for the current Orbiter version. They are derived from the 256 pixel-per-degree versions of the Mars Orbiter Camera (MOC) on Mars Global Surveyor.
What's new are the elevation data. They come from 128 pixel-per-degree Mars Orbiter Laser Altimeter (MOLA) data, also on Surveyor.
Funny enough, although both instruments were sitting on the same probe, their respective processed data turned out to be somewhat lacking in compatibility. The MOC data are mapped into an areographic frame, while the MOLA data use an areocentric frame. It took me a bit of headscratching before I figured that out and came up with the correct nonlinear interpolation. Also, I found a spurious shift in longitude between the two datasets which I fixed by eyeballing. Seems like the research teams operating the different instruments didn't talk much between each other.
Incidently, the MOC data are monochrome (at least the sources I found), so there is no colour information in the textures (other than the fake tint I am applying). Are there any high-res multi-band global maps out there that could be used for colouring the textures?