It is a necessity. I tend to keep too much of the Professor's stuff otherwise. When I see how much I've... erm... borrowed, there's no way out of rewriting the stuff.
I have several colors in my notebook. I switch to a new color every day, just for the fun of it. They're dark colors - lavender black, blue black, green black, bordeaux black, brown black. More than you wanted to know:)
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