I defined the Yellow Tribe as "the 11% who want Scotland to be a completely independent country outside both the UK and the EU [mnemonic: yellow as the background on the lion rampant flag, which this group in my experience is very fond of]", and I speculated that they typically voted Yes to independence and Leave in the Brexit referendum. It's also the group that Wings over Scotland recently called "the unhappy 11%".
They're obviously not a homogenous group. Some members are ultra-idealistic lefties who denounce both the UK and the EU as being neo-liberal conspiracies, others are ethnic nationalists who are romanticising about Scotland's glorious past, and others again are completely average voters who just don't see why either union is needed.
Their preferred way forward was described rather well by Alex Neil in The Telegraph (I'm not saying that he is a member of the Yellow Tribe himself -- he might or might not be):
Top of the list of Scottish demands should be the transfer of the powers being repatriated from Brussels, as they relate to Scotland, to the Scottish Parliament; not Westminster. [...] The accumulation of all these new powers and finances would bring about “neo-Independence” for Scotland, creating the ideal platform for advancing to full sovereignty for the Scottish people in the early 2020’s.
It might sound tempting at a first glance. What is not being said is that it would make it time-consuming and cumbersome to rejoin the EU, because Scotland would in that case have to build a huge apparatus to deal with these power only for them to get delegated back to the EU a few years later.
Because of this, this is a very off-putting prospectus for those voters who prioritise EU membership, including those who voted No to independence two years ago because they thought continued EU membership was secured in that way. This is exactly the group of voters that will be needed to build a winning coalition for independence, so following this piece of advice kicks independence into the very long grass.
Interestingly, I think Theresa May might be eying up the Yellow Tribe, trying to convince them that independence won't even be needed after Brexit. Here's what she wrote in Holyrood Magazine:
As we strike that deal, we have an exciting chance to forge a new role in the world. Scotland’s status will not be diminished by that; it will be enhanced.
Although the Yellow voters only make up 11% of population, they're rather more important within the Scottish National Party for historical reasons. Archive footage of the early SNP events looks like Yellow Tribe meetings. It was probably only when the Independence in Europe policy was adopted in the 1980s that the Blue Tribe began to dominate. However, my gut feeling is that there are many more Yellows amongst the old-timers of the party than amongst those of us who joined more recently.
This is significant because as Wings pointed out, it's a group that desperately wants to avoid an early Indyref2. They want Brexit to be fully implemented before calling a new referendum, and they most definitely don't want to see a ballot paper that asks the obvious question: "Should Scotland be an independent country within the European Union?"
Because they dominate amongst the long-term members of the SNP, it's of course very difficult for the leadership to call an early referendum, because if they do so, their inboxes and voicemail will get inundated by complaints from people who have supported and mentored them since the day they joined the party.
Every political party has a strong instinct to stay united, so if the only way to keep the Yellow Tribe on side is by delaying the referendum till 2025 or so, there's a strong incentive to do so, even if it means the Green Tribe won't be converted to independence and Scotland faces economic ruin in the meantime.
At the end of the day, I find it inconceivable that many members of the Yellow Tribe will vote No to independence next time. They might huff and puff, and they might not pull their weight during the campaign, but at the end of the day they should know that campaigning for an independent Scotland to leave the EU will be easier than convincing people to back independence once Independence in Europe is no longer on the table. However, it will take guts for the SNP leadership to call an early referendum when the Yellows are so strongly against it.