Green tree frog turning brown

[Bennyprib]

I have three GTF and one of them is turning a dark olive colour. The other two are bright green.
They were all bright green when I bought them 3 weeks ago. It is eating well and still active. Is this something I should be worried about?
Their tank is 45x30x30 and is part water part land with a water fall feature and mister.
I feed them dusted crickets.
They are all about 30mm long.
Any help appreciated

 

[Herpetology]

its normal

 

[Bennyprib]

Thank you. Good to hear