Mobs being shaded to match biomes could give some variety to mobs without introducing too much and add some difficulty to the game too.
A similar system that is used for leaves and grass could be used for shading at least some of the mobs and make them feel more biome specific, ex., a darker green swamp creeper. One issue with this system is that creepers and cows are obviously different colors entirely and would possibly require separate shading systems or perhaps some mobs would just have to be left out of shading entirely. To avoid a color changing chameleon affect, mobs should spawn the color of the biome they start in and stay that color. By making the mobs change color to blend in to their biomes would also make it harder to hunt passive mobs and avoid aggressive mobs.
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Here's some images of a creeper and a pig with some more biome specific colors.
A similar system that is used for leaves and grass could be used for shading at least some of the mobs and make them feel more biome specific, ex., a darker green swamp creeper. One issue with this system is that creepers and cows are obviously different colors entirely and would possibly require separate shading systems or perhaps some mobs would just have to be left out of shading entirely. To avoid a color changing chameleon affect, mobs should spawn the color of the biome they start in and stay that color. By making the mobs change color to blend in to their biomes would also make it harder to hunt passive mobs and avoid aggressive mobs.
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Here's some images of a creeper and a pig with some more biome specific colors.
+1
But this is not bad idea..