Interestingly enough I've received quite a few emails asking me what color of pen I use to correct and grade papers. Apparently it's considered politically incorrect to now use red as it can hurt a child's self-esteem as it's considered negative.
My mother had mentioned this at one time and I pretty much laughed it off. I've never taught anywhere where anyone told me what color to grade with and I've taken a course where anyone told me what color I grade with. And quite honestly, most of my students are too busy thinking about skateboarding, sex, movies, sex, girls/boys, sex, lunch, sex, music downloads, and sex, that I doubt they even read, much less notice, what color I've written in.
That being said, I grade in whatever damn color I can reach first. I've graded in red, blue, pink, purple and green (I tend to like green; it's my second favorite color). I've graded in highlighter pens too, which are a lot of fun. Sharpies are cool in terms of color (the lime green is fun) but they bleed through the paper so I tend not to use them.