Direct sunlight cased shells to darken

[fgately]

I am the very happy owner of three Russian torties. I bought them from different petshops. One male (Boris) and two females (Daisy and Zuzu). I seem to have noticed all of their shells became quite a bit darker pretty soon after i had them in natural sunlight. They are super healthy and are eating lots of good stuff.

Is the darker color change a normal thing? I assume it has to do with the nautural sunlight, and may be the need to be a bit darker to help absorb the morning heat.

I love when they wander over to the first sun that hits the yard, and stretch out to warm up. Looks like they are on vacation!