Not sure of the blue color, but I'll go with Sven's explanation (good work Sven!).
There was also more than 1 generation of the Sabre. Not sure if the earlier version was called a "I" though (verses a "II"), but there was some sort of improvement, or second generation, in the Sabre line. I think the newer/later Sabre was supposed to go deeper, but some of the hardcore fans and techno-buffs claimed that there was a compromise in the averaging ability of the later versions. In the earlier versions, they supposedly average in and around iron better (thus made better ghost town machines, for instance). Perhaps they didn't go as deep, or perhaps they were weak on larger iron or something, but they excelled in seeing through small iron (as all two-filter discriminators do, to some degree) better than their successor.
In general, any sabre is just going to be a simple to use 2-filter discriminator. They are not very deep-seeking (when compared to power-house machines on the market), nor will they work in mineralized soil, or mineralized wet salt very well. But when used in certain land environments, can run circles around power-house machines. These type hunt locations would be ghost town type hunting where nails abound (and depth and mineralized soil isn't really an issue), or urban demolition sites brimming with iron cr*p, etc.... They also lack TID. But for relicky dig-all type sites (urban demo's, ghost towns, ruins, etc...) a hunter will gladly sacrifice that to see conductive targets amidst bountiful nails.
