Where the shape comes from
A person shown large, standing close over a fire, the flush of its glow read as the colour itself — one of the oldest words for red, later stretching to bare, naked, stripped down the way skin flushes bare and red near heat. It gives 赤字, a deficit, red figures in the ledger, matching the Western habit of marking a loss in red, and 赤脚, barefoot, bare feet touching the ground directly.
汉字 filed under 赤
No published character on HSK Guide is filed under this radical yet. 汉字库.