Since the default quest tracker (or log) does not show quest levels, I assume you're already using a quest-related addon if you're seeing levels you'd like to change the color of. Why not ask its author to add these features?
Yes I do use an addon currently that shows me the level of the addon. But I am taling about all the text for that quest to change color. Also all the quest addons out there that have any tracker control are way to bulky for some. I am looking for something that is very basic and simplistic in design. I also want to be able to track quest I want and not what these addons want. The one addon that kinda did this (questfu) I had to stop using because the author stopped updating it.