In the Watchtower Society’s 1988 reference book, “Insight on the Scriptures” Vol. I, it says this on page 1146:
“In the apostle John’s symbolic vision, the glorified Jesus Christ is
depicted as riding a white horse and as being accompanied by an army,
all of whose members are seated on white horses. This vision was
revealed to John as representing the righteousness and justice of the
war that Christ will wage against all enemies on behalf of his God and
Father, Jehovah. (Re 19:11, 14) Earlier, Christ’s taking kingly action
and the calamities that follow are represented by different horsemen
and their mounts. – Re 6:2-8.”
To get more details on the Revelation 6:2-8 verses which are specifically asked about in this question, I found this explanation in the Watchtower Society’s 1969 book, “Then is Finished the Mystery of God”, page 40:
“In this preliminary vision the rider on the white horse differs in
appearance from the rider of the white horse described in Revelation
19:11-16, where this same rider is pictured as having ‘many diadems’
on his head and as having protruding out of his mouth a sharp long
sword with which to smite the nations of earth, to pronounce the
execution of divine judgement upon them. However, in this latter
vision the rider of the white horse is riding to the ‘war of the great
day of God the Almighty’ at the place that is called in Hebrew
Har-Magedon… But when the rider on the white horse appears with his
bow after the opening of the first seal of the scroll it is at the
beginning of that ‘time of the end.’ That is when the seven Gentile
Times have ended, and hence it was the early autumn of the year 1914
C.E…”
This indicates that the Jehovah’s Witnesses interpret the first rider of the Four Horsemen of the Apocalypse to be Jesus Christ from the year 1914 and onwards, and that they also interpret the rider of the white horse in chapter 19 verses 11 and 14 to be Jesus Christ, but that ride is still future as they say the battle of Armageddon has not yet begun.
On page 44 the author of that 1969 book goes on to confidently state that,
“Worthy ones of this generation of mankind will see the crowned Rider
of the white horse complete his conquest with the help of Jehovah God
the Almighty.”
However, given that a generation is about 36 years or so, that generation has NOT seen the completion of Christ’s ride. He then admitted to previous interpretations not being too precise either:
“In July [of 1917] the Watch Tower Bible & Tract Society published the
book known as the seventh volume of the ‘Studies in the Scriptures’.
(See the issue of August 1, 1917, of ‘The Watch Tower and Herald of
Christ’s Presence’, page 226, column 2.) This book contained a
commentary on the entire Book of The Revelation, and attempted to
explain, but too soon, Revelation 6:1, 2. However, thirteen years
later, or on August 11 of 1930 the Watch Tower Society released at its
Brooklyn headquarters the two volumes of the book entitled ‘Light.’
Ah, at last this set forth the explanation of Revelation 6:1, 2 that
was based on events since the end of the Gentile Times in 1914, which
events fulfilled the thrilling Bible prophecies.”
After saying the year 1914 was only identified in 1930, with hindsight, as the time Jesus began to ride forth as per Revelation 6:2, the ‘Then is Finished the Mystery of God’ book goes on to give its interpretation of the three other horsemen, from pages 46 to 76. Here are just brief quotes to summarise Jehovah’s Witnesses beliefs about them:
“The horse that John now saw come forth was ‘fiery-colored,’
flame-colored, red like blood. Its color suggested blood! Very
appropriately so, because it fitted in with the mission on which the
horse’s rider rode, namely, ‘so that they should slaughter one
another.’ Besides this, since it was granted to the rider ‘to take
peace away from the earth,’ what could this mean but war, bloody war?
So, then, when the Gentile Times ended in 1914 and the Rider on the
white horse did ride forth, was this event marked by bloody war? Yes.
World war, the first world war of human history!” Page 50 “The crowned
rider of the white horse took no part in World War I, which was
started by the second horseman armed with the ‘great sword’.” Pages
51-52
“The horseman that John now saw was on a black horse... represents
famine, food shortages… After the outbreak of World War I and the
ending of the Gentile Times in 1914, this is exactly what happened.”
Pages 52 & 54
“A fourth figurative horseman dashes onto the scene of world affairs.
His horse is yellowish pale, livid, sickly-looking in color. What a
good match its color was to the name of its rider, whose name is
Death! …This is premature death… the symbolic rider Death was
accompanied by Hades… Those brought down to Hades by the fourth
horseman Death were to be many… something that would be an added proof
of the fact that the first horseman, Jesus Christ, had been crowned
and had begun to ride victoriously since the close of the Gentile
Times in 1914 C.E.”
and then refers to the Spanish influenza of 1918-19 which killed some 20 million victims. Pages 56 to 59.
The key point in the Jehovah’s Witness interpretation of the Four Horsemen of the Apocalypse is the date October 1914, upon which all of their interpretation depends. If they are wrong about that, they are wrong about all else. So far, they are sticking to their doctrine about October 1914, but if that is dropped at any time, then they will have to reinterpret their claims about the Four Horsemen of the Apocalypse.