In theory, you could make the blood whatever color you want if you hack the game and replace the blood textures. Or the palettes, if it's 8-bit (odds are the blood textures are the same, but the saturn merely switches pallets to get green or red blood).
well, you could make your own code using the method described in the readme.txt that goes along with the comms-link package! (provided you have a comms-link card of course) Just start the game with its master code, keep the blood green, dump all memory and then turn the blood to red, dump the memory again, and run a binary comparison. Voila! If everything goes well you have one byte that's different, and you'll need to set that as an AR code. If I had HotD i'd do it myself, but alas.
Cheers for the replies fellas, I'm can't program to save myself. I was just looking for something easy and executable, like the language patches made for a couple of games a while ago... obviously, it dosen't look like there is any available. damn!
m3d10n, your guess was right, the blood colour change is not in the textures, its just done via the palette, in the original work on HotD, it was being coded for red blood and the textures were created accordingly, there was lovely red and magenta and pink shading to make the textures look like big chunks of meat flying everywhere!! when sega gave the order for green blood, the textures were re-done and they were optimized for green hence when the palette is changed to red, it dosen't look as good as it did when work originally started....