My Greek tortoise's shell got darker over the past year

[I Love Tortoises]

Hello guys. I have a Greek tortoise. He is very healthy but i have noticed that his shell got darker over the past year. Why did that happen? Is it because of growing or is it a medical condition? Any help would be appreciated. Thanks.

 

[wellington]

It's all normal. Some get lighter most I would say get darker. Nothing to worry about.