In his Medieval Hymns and Sequences, John Mason Neale identifies roseate as the pale color of the last drainings of life-blood (“as everyone knows”, he says) since though one drop would suffice, Christ shed all.
An 1895 agricultural bulletin from the University of Michigan defines roseate, rosaceous as “rose-red; a pale blood-red”.
From Harry Irving Greene, a popular novelist and short-story writer in the early 1900s, here’s another reference associating roseate with blood. It reads like a fictional vignette designed to tickle all the sentimental reflexes in the folks “back home.” It appeared in newspapers in May 1918.
Father: This wonderful letter that I am writing you - a miracle letter. I was hurt, badly, but I am going to get well. It happened like this — you know I am I an not allowed to name place or date.
No Man’s Land! We were raiding it by night, three of us — scouting, prowling. It was as dark as the dungeons of inferno, but often they sent up signal shells — roseate, bursting things that bathed all that evil land in a blood-red light. When their glare flared over us we had to stand as we were caught, hand or foot upraised — moveless objects in the red glow until the light snuffed out and all was dark once more.