You DO NOT want to use Red loctite. In order to remove it without damaging the part, you would probably need to use heat.
Blue loctite is my choice for firearms related attachments that are NOT directly associated with optics. As an example, the screws mounting a Weaver or Picatinny rail get "blue" - which is 242.
My go-to for putting scope mounts/rings onto rails, and just about any other optic-related choice is Loctite "Purple", also known as "vibra-tight". That's Loctite 222 for anyone that doesn't want to get cross-threaded. I find that you can use a little bit more, spread out evenly, and still get good results. Also, you are able to break it free with less risk of damaging fasteners should you need to.
My general practice is to remove the rails, degrease, and then re-attach with Blue. Once that has set, I will put on the rings or mounts, put the scope into place, and carefully torque everything, and verify with a quick boresight that things are close to lining up. Once that is done I begin the process of loctite, one bolt or fastener at a time. I'll remove the bolt completely, apply the loctite, and then re-fasten and re-torque. Normally this makes sure that the entire mount is correctly in place and evenly torqued when you are done.
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