The Minecraft turtle seems to be loosely based off a Green Sea Turtle.
The default texture looks nice, and I enjoy it, but it does seem overly simplified.

If you wanted something a bit closer to a real Green Sea Turtle, then look no further!

I have taken careful consideration when creating this mob skin so it can be as accurate to it's real life counterpart as possible whilst still retaining that Minecraft feel.

Keep in mind that this species can be quite variable with how they look as they have natural variation between individuals and with them being a widespread species, there are many subspecies all looking slightly different. I have tried to go for the more generic Green Sea Turtle look to get the best representation.