It's the colour of the Protestants. The native population of Ireland is largely Catholic, and later on the Protestants came to Ireland and were supported by the English in their oppression of the native Catholics. Of course this is a little early for that, but even still red at this time was associated with the English, who were slowly taking over the country. Liam lost several of his family members to the clan wars against English neighbours who were propped up by Templars.
Hm... this whole orange thing is interesting and reminds me of the Orange Catholic Bible featured in Dune. Frank Herbert (author) was raised Catholic, but American -- his novel The White Plague takes place in Ireland, so I'm wondering if there is a family connection there. However, Dune takes place 8000 years in the future, so it's certainly possible that he did some combination thing of Protestantism and Catholicism for his own purposes. (This is by no means a major feature of the novels, only a very minor component. But I was always curious about the "orange" part.)
Ok this is actually really adorable in my opinion XD As usual a great attention to detail, right down to the white pattern on the OC's cuffs, and that playful smile on Ezio's face UGH. Its almost like he's saying "Lol try again!" XD <3