Of course! You can do whatever you want for your Christmas paper borders. As you are the ones who will use the paper, you should suit the design with the purpose. For example, you can make the borders for language exercises and they relate to the topic of Christmas. And for the paper borders for children, the color should be milder than the ones for Christmas diner invitation. As for the letter for Santa, there should be some pictures of Santa or the color of the paper is a bit rustic.
Christmas paper borders are inserted to decorate the paper. The paper can be used for many different purposes; Christmas greeting cards, wish lists, letters to Santa, and so on. You can exchange regular greeting cards with paper to get more personal messages. Teens and young adults like to use the paper for writing wish lists and to list the names who have received the Christmas gifts. Some adults also write Christmas shopping lists on a paper with Christmas-themed borders. The borders are indeed useful to mark Christmas papers.
People who usually make the templates are adults, but children can make the ones too. Most children will use the paper to send a thank you letter to their parents and teacher, as well as to Santa for the gift. If they are already teens, they will make the paper borders to write a wish list and learn about graphic design. In fact, most parents make the borders for the children, and then they themselves reply to the letter back. In short, adults are the people that make the templates; can be your teachers or parents. Then, children or teens can make them too for their own needs at Christmastime.
Actually, you are free to color and decorate the Christmas paper borders. For the borders themselves, the ones you can color are for home exercise for children from their teachers. But if anyone wants to add the color, you are free to do so. There is a personal value if you color the paper yourself. In fact, you can make a sort of code, so that you know the purpose of the paper. After all, if you make the paper borders on the computer from scratch, you are technically color the clip arts and all drawings to insert on the blank page.