It used to be recommended back in the days of Jordache and Gloria Vanderbilt in the early 80’s to keep the dark blue indigo, dark blue. Now faded jeans and acid wash are more the style so you don’t hear it anymore.
I have never heard of anyone doing this. I try to wash printed t-shirts inside-out in the possibly vain attempt to save the designs for longer, but it never would have occurred to me to wash jeans inside out!
Yeah, I tend to agree with @gailcalled. I think if there’s any difference, it will be in the amount of abrasion (fabric to fabric) during the wash. I’m not sure that means you’d be better off with them right side in or inside out, though.