I could see a freeblade knight being granted the right to take on a chapter's colours. But yeah not for me.
How about knight houses during the heresy? Did they adopt forge world / Titan legion colors?
House Malinax seems to have adopted the colors of Xana II for example.
In the case of House Malinax, they were an ex-Knight Household based around a specific bloodline (they may have had a different name also, it isn't clear, but it seems they had mostly died out). Xana II essentially resurrected the House, and the new Malinax Knights were sworn to their service.
The scorpion logo you see on Xana II forces is actually the original Malinax logo. The scorpion device was altered slightly by adding the triple tail (to represent it being 'transmuted by the omni-thingy'), and it seems it was adopted across all Xana forces presumably as a sign of the bond between Xana and Malinax.
The 'colour', is part Xanite tradition, and possibly religious rite? It's bone coloured because Xana is inhabited by several large 'megafauna', who are hunted and their skeletons used to 'paint' the Xanite war machines.
It seems then, as though both informed the heraldry of the other?
Taranis Knight's on the other hand were, pre-heresy, actually blue. But clearly adopted the Red of Mars sometime around or post that period after nearly being entirely wiped out.
I certainly can't think of any in fluff who take Astartes chapter, or titan legion colours though.
Edited by Stray, 17 July 2019 - 02:07 PM.