Creepier Creepers

Creepers, although a mistake, are probably one of the most well know mobs outside of the Minecraft Community. When first created they were coloured green to camouflage
into the old Minecraft grass block and blend into the foliage. Hence the name, creeper.

If you look up the old Minecraft grass block texture you can see it is a lot brighter and resembles the creeper a lot more. Although the creeper is still the same colour as the new grass block, green, it doesn't resemble the same shade, and this is a mix of new biome grass colours and new texture updates. It's quite easy to see a creeper from a distance in some of these biomes, like mountains and swamps in particular. 

My suggestion is that when a creeper spawns, the shade of green is determined by the biome it spawns in. This would add back that "I can't see it!" atmosphere and give the game a little more excitement. At the moment I would say a spider is harder to see than a creeper in some scenarios.