Would you like to paint this room:
A)white; or B)another colour?
Blue wasn't mentioned by anyone at the time.
That's not actually correct - in the government document linked to in the other thread (the one that SodaPoppins' is referring to?) - blue (WTO/no-deal) and several other shades of Brexit are discussed in some detail:
"1.1 This paper looks at the potential models for the UK’s relationship with the European Union, if there were to be a vote to leave.It provides examples of countries that are not members of the EU but have other arrangements with it–specifically Norway, Switzerland, Canada and Turkey–and describes those arrangements."
"It also looks at a possible relationship based only on World Trade Organisation membership." ...
"If we could not reach agreement with the EU on a new arrangement, our trading arrangements would revert to WTO rules.This would provide the most complete break with the EU."
"(c)WTO membership.The UK, like all other EU countries, is a member of the WTO. If the UK had not agreed a new relationship with the EU by the time we left, then we would revert to our common membership of the WTO as the basis for trade–just like Brazil does in its trade with the EU."
Of course, the government warns against choosing any colour other than white (and especially blue) but the Leave vote won nevertheless - and the blue tin of paint was definitely in the basket at the till.