Question about monster palettes

Greetings.

I want to ask about monster palettes. I am developing a mod that changes randomly the monster palettes at the start of the battle. The objective is to individualize monsters based on different palettes.

The palettes in the game use the RGB scheme of color. Technically it is only the matter to change the values related to the red, green and blue channels. However, in pratic, it can't be done randomly. It must be done with a algorithm designed for the target graphics. Otherwise it will  generate undesired colors that will make the monster graphic trully ugly and unwatchable.

The issue is that the monster images use a shading technic where black, white and ash-alike colors are used to create light and darkness. It  gives the sensation of depth in the image. So if i want to preserve it I must not change those specific colors. As example, black (0,0,0) and white (255,255,255) must not be altered. Two algorithms can watch this requirement: rgb swap and mono recolor.

The rgb swap algorithm is to randomly swap the values between the red,  green and blue channels. Simple but can only generate eight variations of colors.

The mono recolor algorithm is to transform the image in a monocromatic one and then recolor it. Technically it calculates the smaller and the  bigger values from the RGB values. Then setups the new values for the RGB channels as a random value between the smaller and bigger values. It has a bigger variety of colors but it also has the tendency to generate color in the black-ash-white tonality.

If you want to check it in practic you can download it here: Minion Colors.  Aply only one of them in a ff3 us 1.0 rom with a header. Then go fight somewhere like the Veldt, as example. If you fight at the Colosseum you can see the original colors before the actual fight in the Colosseum sub-menu where you select characters.

Does anyone know a better algorithm for those specific monster graphics? I don't belive I can create/find another recolor algorithm that work well with them.

Another question is that two or more monsters in the same battle with the same graphic use the same palette. I want to each monster with the same graphic to have different palettes. Is it possible or there is a hardware limitation? My first throught is that all monsters should have a individual palette in-battle but  apparently it looks they are shared for the same graphic instead of individually by enemy.