One whole shelf in my office library is full of Bibles of many different versions. The one I use the most, the New King James version, has the words of Jesus in red.
One theologian I read said that this is a travesty. By raising the words of Jesus above all other scripture, you naturally lower the value of the other words, he says. All scripture is inspired by God; therefore, all the words are of equal value because they are all God's words.
I don't know how you feel about that. You probably take the more common position that it is nice to separate the words of Jesus for identification purposes.
But here is my personal take on the matter. When I try to follow what Jesus taught, I find that I am woefully inadequate and powerless for the task! I mean, who can truly forgive his enemy, let alone love him? The good news is that through His death and resurrection, he accomplished for me what I could not accomplish for myself - on my best day!
So, His words are in red, because they leave me owing; i.e., in the red.
Then comes his sacrifice for me, and now I have all I need, in Him, to overcome and be successful; i.e., in the black.
In the Gospels, He removed my debt - the red; and in the Epistles, I am on victory ground - in the black.