What an interesting question - Peterhead, the largest whitefish landing port in the UK, and Scotland's most easterly point, is certainly locally called the 'Blue Toon' (Town).

As for where it came from, Dougal (who has North-east connections, coincidentally), has always thought it was linked to the name for the Peterheid folk: Blue Mogganers. So what are moggans (or moggins)? Well, that's an old Scots word for stockings. The Concise Scots Dictionary says this can be a footless stocking or even just a coarse protecton for the legs, but I think we can asume it was worn in a sea-boot. Apparently, the local knitters used or at least favoured blue wool. [There may be a connection here with the local fisherman's gansy (jersey), also usually knitted in blue]. Anyway, the name seems to have something to do with the colour of old-time fishermen's socks!