Colorblind God

Thomas and Rebecca were brother and sister. Rebecca was the older of the two. They lived in a small village in the East of England. It was a quiet place. Not much happened there. Their Mother would drive in to London to work and their father would drive out into the countryside to paint. They would often complain that nothing exciting ever happened.
Then one day in the summer, after their parents had left, the mail came. Thomas brought the mail in from the mailbox, and noticed something interesting! Two letters were rolled up like scrolls, and kept closed with wax.
“Rebecca,” he said.
“Yeah?” she replied, putting down the book she was reading. It was the last Harry Potter book.
“Could you read this for me?”
She really wanted to finish her book, but she got up anyway, saying, “okay.”
So she looked at the first scroll. Her name was scrawled in big old letters, with ink so thick that it stood off the page. She looked, and on the other was her brother’s name!
“They’re for us!” she said, forgetting The Deathly Hollows, and pulling off the red wax seal from her scroll. Thomas did the same to the green seal on his.
“Dear Rebecca… that’s me,” she read absently, “This letter has been sent to inform you that after 16 centuries Arthur, the Bear of England, the Holder of Excalibur, Eagle of the Shores, and the King of the Britons, is returning, and you are cordially invited to the welcoming ceremony. Tea and biscuits will be served.”
“This is exciting!” said Thomas.
“Yeah… but… what does one wear to see a king?” thought Rebecca.
“Well,” said Thomas innocently, “probably something that is the King’s favorite color.”
“Which would be red,” said Rebecca.
“Why?” asked Thomas.
“Because the wax is red of course,” said Rebecca.
“But mine is green,” said Thomas… and then added, “So I’ll wear green.”
“No,” said Rebecca, “Arthur’s favorite color is red.”
And so it went until the day of the return, Thomas saying green, Rebecca insisting on red. After a time Rebecca decided Thomas would be thrown out for wearing green, and Thomas decided Rebecca would be thrown out for wearing red.
And then the day itself came. Rebecca wore her very best red dress, and matching red shoes. And Thomas wore a green waistcoat with matching green tie.
Their parents drove them to the party and let them off. “We’ll be back to pick you up at 8,” said father.
“Have a good time,” added mother.
“We will,” they said.
And so they went to the gate and presented their scrolls to the doorman, whose name was Lancelot.
The building was packed.
“Look,” said Thomas, “William Shakespeare is wearing green tights, I was right! Arthur likes green.”
“But look,” reposted Rebecca, “Princess Diana is wearing red.”
And on it went Thomas pointed to Cromwell, Queen Victoria, and John Lennon . Rebecca pointed to Churchhill, Darwin, and Isaac Newton.
“One of us has to be wrong,” said Rebecca.
“Yeah,” agreed Thomas.
“About what?” asked King Arthur in his deep old voice, cracking with centuries of absense. He had stood behind them, unnoticed.
“What’s your favorite color?” asked Rebecca.
“You’re going to throw her out aren’t you?” chimed in Thomas.
“You are wearing different colors?” Arthur asked, astonished, “I am color blind. You both look the same to me. You are both equally invited to this party.”