Which is the usual procedure when you have had a rifle rebarreled and have a new walnut stock you want it bedded in, to blue the barreled action first and then bed the barreled action or to bed the action in the new walnut stock first and then reblue the barreled action?

Bluing is the LAST thing you do

Amen ..
inlet it, add your barrel accessories, if you want to bed it, bed it, and if you want to float it, float it ..

once EVERYTHING is done, then blue.

Definitely bed it first. What if you blued it and then touched it with the sand paper while trying to get the fit "just right". Looks like scratches to me.