nitchibutsu/shettle.cpp - Change shettle palette PROM decode to match wiping

[mamehaze]

No description provided.

[mamehaze]

this doesn't match the reference shots provided, but it's very easy to incorrectly hook up r/g/b on a PCB anyway.

[mamehaze]

With the changes it looks like this

The fire effect on the shuttle is red/yellow (logical colours)
The handle of the axe is brown, the blade is grey (logical colours)
The torchlight is yellow (again a more logical colour)
Skin of character is a shade of pink
You can much more easily read the numbers on the flags when you collect the items
Corridors are a blue/grey colour, which fits the 'space' theme.

[mamehaze]

The existing PROM decode gives the following, where none of those colour choices seem logical

[mamehaze]

while neither match the PCB output shown at https://www.mameworld.info/ubbthreads/showflat.php?Cat=&Number=398233 I strongly suspect it's just hooked up incorrectly there. (R and G are swapped, and I'm not sure there's any Blue output on those PCB shots at all, strongly suggesting the adapter isn't correct)

[mamehaze]

alternatively just using the wiping decode looks a lot better too, giving a more realistic skin tone. given how close the rest of the driver is to wiping I'm be inclined to use that. The wheels on the enemies have a metallic grey look this way too, which again seems more correct. The 'axe' graphics end up more blue, but that's a realistic enough design choice.