I defined the Blue Tribe as "the 33% of voters who want Scotland to be an independent country inside the EU [mnemonic: blue as the Saltire and the EU flag]".
The Blue Tribe of Scotland encompasses a spectrum of people, ranging from people who're closer to the Yellow Tribe and are relatively happy to put up with an independent Scotland being outside the EU so long as we get independence, to people who're closer to the Green Tribe and only want to see Scottish independence within Europe, not without.
The Blue Tribe is the only one of the four tribes that has lost two referendums in short order, first the Indyref and then the Brexit vote. As a result, many of its members are getting a bit paranoid and are wanting to play it safe, calling Indyref2 only when victory is practically ensured. Although I'm a Blue myself, I do wonder whether this ultra-cautious approach is going to cause us to miss the boat by delaying the next independence referendum for too long.
Both the SNP and the Green Party are dominated by the Blue Tribe. However, the SNP also contains most of the Yellow Tribe, and the Green Party also contains a good number of Green Tribe members, so it would perhaps be more accurate to think of the SNP as a Yellow-Blue Party and the Green Party as belonging to the Green-Blues. As a result, the SNP is now perhaps finding it harder to rally all its members behind a new referendum than the Green Party.
It would probably be fair to describe the Blue Tribe as internationalist civic nationalists, and most of its members are probably as far removed from ethnic nationalism as you can get, which of course made them rather angry during the last Indyref when they were accused of being blood-and-soil nationalists.
So although this tribe is the one which has dominated Scottish politics for the past decade, its members are feeling rather paranoid and under attack. This will probably not change till we win Indyref2.