1802, "having red or reddish blood," from red (adj.1) + blood (n.). "Specifically noting the higher worms, or annelids, in which, however, the blood is often greenish" [Century Dictionary]. The figurative meaning "vigorous, spirited" is recorded by 1862.
The children born in California are certainly a great improvement upon those born among us. Nowhere can more rosy specimens of health and beauty be found. Strong-limbed, red-blooded, graceful, and as full of happy animal life as young fawns, they bid fair to develop into admirable types of manhood and womanhood. [Bayard Taylor, "New Pictures from California" 1862]