In a world were the only colors you can see are the same as your soulmates eyes, it was unusual that people see more than 1 or 2 colors. But, then again, when has Shirou ever been normal? With the ability to see 3 different colors, how does this affect the Holy Grail Wars? This is the story of the sword that wants to be a hero.
For as long as he could remember, Gilgamesh could only see 3 colors. Gold, orange, and green. He knew that he most likely had 3 equals, 3 people that could stand by his side in all things, so when he died, not able to see the rest of the world's colors he took it as an insult and determined that he would never find those equals. This is the story if a lonely king.
All Tsuna ever wanted was to be normal, but with the fact that he could see 2 more colors than most people, he dispared, not that it stopped him from trying to find the other parts of his soul. But when Reborn came along it stopped the search in favor of survival. This is the story of the most normal of the 4, and the sky that accepts all that travel between it and the eath.
Harry was as broken as one could get. With the realization that Ron and Harmonie were paid to be his friends, and that Dumbledore was minipulating him so that he myrtared himself so he could swoop in and claim the glory, he tries a spell that would form a mental bond between him and his soulmates, so that they can here each other's thoughts. This is the story of a desperate mage.