Yes, SOME prisons and jails allow haircuts, style and even color. Cuts are usually free but coloring will cost.
There was a show on TV some years ago, where the prisoners were taught the skills of hair cut, color etc. It was interesting how they had to sign in and out for combs scissors etc. Since it was about beauticians, the lady prisoners were extremely proud to be chosen to go to school and cut hair. A future for them on the outside.
Not all prisons allow this, however most of the men always seem to be well groomed. Of course there are some who have wild hair. The ladies don’t seem to bad off but I seldom see any going to trial have their hair colored.
The link below is generic and interesting…hope it helps answers some questions.
to know about the jails that Vallow and Daybell are in, there may be a handbook on line.
I do remember, that the prison, felon Jodi Arias is in, all inmates with long hair have to have it pulled back into a pony tail so their entire face can be seen. I got that info from one of the many posts here, years ago! It may be the same for Idaho jails and prisons.
https://prisoninsight.com/can-you-get-haircuts-in-prison/
and I edited because spell check decided to put it other words then what I typed!