A Merry Christmas to you and yours too!
Where a man at arms possessed his own coat of arms he would display them, instead of a livery jacket. Otherwise he would bear the livery colours of whoever's retinue he belonged to... if he wore any.
It also appears that the men in a retinue might wear the retinue of their lord when engaged purely on his service, but when that lord was a retainer of another and acting for him, they would wear that lord's colour(s) instead.
So for example Sir John Howard would wear his own coat of arms, as would any men retained by him who had them. Sir John's own household wore black. Sir John was also a retainer of the Duke of Norfolk and would have contracted with him for 'x' additional men on top of his household, all to be decked out in Norfolk's livery and not his own. Sir John's contingent would therefore consist of a small core of men in black (with perhaps a 'bend' - a shoulder sash in Norfolk's colours worn over that), with the remainder in Norfolk's colours.
That at least is my interpretation of how it worked
