Hi, and welcome.

That vein thing is a little weird. Maybe someone else has an answer.

They are nocturnal, so he is likely to stay in the same spot all day. Try to observe him at night. Sometimes mine will go to the exact same spot to sleep, but at night they are all over that tank. The brown color could be because of stress or because of something environmental. He may just need a few days to settle in.He's eating, so that's good. Are you finding any poop? Is he spending a lot of time in his water dish? Is he going for the crickets immediately?

I would lean more towards him needing to settle in, but I don't know about that vein thing.