You didn't ask me, but I'll reply anyhow: Loctite blue is usually used on on threaded parts that you plan to disassemble at some point in the future using ordinary hand tools. Examples on bikes are just about everything that may loosen due to vibration, with the exception of that darn pulley nut on our bikes that is also prone to loosening (Red on that puppy). Depending on the size and grade of the nut and bolt, Loctite red has super holding power, and may require heating to effectively remove, if ever. Oh, and I hate it when people use the wrong product for the application!
Ex: this weekend I picked up an "overly customized" M50 Suzuki Boulevard where the prior owner had used Loctite red on the wrong parts. While taking off the ugly aftermarket mirrors (some chromed pot metal, inferior pieces of poop) I began working the attaching studs out when the left one snapped off flush in the clutch perch. S#@t! I could now see, on closer inspection, that the prior owner had used Loctite red on the threads...Ugh! No great loss though, as the mirrors mere really ugly, the clutch lever was damaged and required replacement anyhow, and a used manual clutch lever assembly (inc. perch) for this bike was only $10.00 shipped. If it would have happened on the hydraulic brake master cylinder side I would have lost a good deal of my profit on the bike, or been forced to drill the stud out and hope I didn't mangle the threads in the process Most nuts and bolts on our bikes are lighter duty, certainly not "grade 8" and Loctite red is just the wrong product for most of the fasteners I have found. When in doubt, the factory service manual normally gives info on the right thread locker type by fastener application.
In the absence of other information, just ask yourself if you will need to remove the part in the foreseeable future using hand tools. If the answer is yes, Blue is the choice. If you answer no and really need it locked in there, go red. But plan to use heat whenever you go to remove.
PS: Not being snarky but I have been forced to use more Loctite red on certain Harley parts than I really wanted too, due to excessive vibration and fasteners falling out otherwise. Luckily HD tends to use a better grade of fastener that holds up to heavier wrenching that most Japanese bikes IMHO.