Or the other way round: They hardly move, hide, sometimes show extremely brilliant colours.

Ohter species do react with increased aggressivity or "false tameness".
In some cases, a special stress colour appears and sometimes, this may stay the only sign of stress.
In other cases, bad shedding or occasional trembmbing attacks are the only sign.

And there is much more...

I hence would not say its always simple to detect stress in lizards. Even after several decades of herpetoculture, I sometimes have problems in deciding if a lizard is stressed or not.

Regards

Ingo