Yesterday, my five-year-old nephew was assigning characters from the Easter story to the rainbow of marbles in his marble run, and he chose the red marble (his favorite color) for Jesus. My sister commented on how his choice mirrored D&C 133:48 (and Revelation 19:13), which says Jesus will be wearing red at the Second Coming.
That got me thinking of colors that symbolize Jesus. Personally, I’d have picked the blue marble, for living water. What other colors would symbolize Jesus? (Please add more colors/references in the comments!)
Red: I have trodden the winepress alone (Isaiah 63:3). And the Lord shall be red in his apparel (D&C 133:48). And his sweat was, as it were, great drops of blood falling to the ground (Luke 22:44).
Orange / Yellow: For he is like a refiner’s fire (Malachi 3:2). They presented unto him gifts: gold, frankincense, and myrrh (Matthew 2:11). His eyes were as a flame of fire (D&C 110:3). I am the light of the world (John 8:12).
Green: I am the vine, ye are the branches (John 15:5). If these things be done in a green tree, what shall be done in a dry? (Luke 23:31). And God said, let the earth bring forth grass…and it was so (Genesis 1:11).
Blue: The water that I shall give him shall be in him a well of water springing up unto everlasting life (John 4:14). If any man thirst, let him come unto me and drink (John 7:37). Jesus went unto them, walking on the sea (Matthew 14:25).
Purple: And they clothed him with purple, and plaited a crown of thorns (Mark 15:17).
Little nephew, whatever favorite color you bring to Jesus, I believe it’s one of His favorite colors, too. Jesus is Lord of all creation, and He sees Himself in every color of the rainbow.
By Common Consent, a Mormon Blog 
Obviously a full rainbow! Because Jesus embodies the entire ROYGBIV light spectrum!
John8:12 “Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life.”
I like Carolyn’s full rainbow answer because yes, he is the creator of all and you need the full rainbow to express that. But, I might also pick ultraviolet because Jesus and the atonement is so far beyond our understanding, just like ultraviolet is beyond our ability to see. Or maybe even infrared, because that is warmth and love.
Red — The blood of sacrifice
Orange — A purifying fire.
Yellow — Gold with the dross removed.
Green — The resurrection and the life.
Blue — The waters of baptism.
Indigo — A royal heir.
Violet — The robes of royalty.