Fr. Herman Kramer's 1956 The Book of Destiny is the most recent Catholic commentary on the Book of the Apocalypse. He covers the White, Red, Black, and Green Horses in part III, §A, chapters 1-4.
The White Horse coming first on the scene is an allegorical figure of Conquest and of apparent victory over the Church. … the white horse was a symbol of victory won by the help of the gods … Some interpreters hold that the rider on the white horse is Christ Himself, (Iren. IV. 21/3; Victorinus and Andreas followed his opinion) and they remind us of chapter XIX. 12, where Christ appears riding on a white horse. Others hold that the white horse symbolizes the victorious Gospel, and the rider represents the preachers of the Gospel throughout the world.
A Red Horse, the symbol of war, appears.
A Black Horse appears. The description fits the personification of famine. Famine with exorbitant prices for food follows in the wake of war.
A horse of so strange a color appears, that the Seer calls it a "Green [or 'pale'] Horse". The color suggests to the mind a body decaying with pestilence. Death rides the horse. This personification of death presages utter depopulation or DEATH for this "FOURTH PART" of the earth.
See Fr. E. Sylvester Berry's 1921 The Apocalypse of St. John pp. 69-70 for a much briefer account than Fr. Kramer's.