真っ赤

Etymology
Compound of.

First cited to the mid-1400s.

The sense arose from the way that something purely red is obvious and clearly visible.

Adjective

 * 1)  extremely red, purely red, very red
 * 2) bright red; flushed
 * 3) deep red
 * 4)  outright, downright
 * 1)  outright, downright

Noun

 * 1) extreme red, pure red, very red
 * 2) bright red
 * 3) deep red
 * 4) outrightness