Sei generally uses two styles of hair: Shuyin Hair (old favorite) and Messy Crop Hair (new favorite), which can be used in the aforementioned colors. Please only use these colors (or as close to them as you can get). You can mix and match any hair to suit your drawing preference, however.
For eyes, Sei has always used bright eyes. They can be either black or blue (though I prefer blue).
For bonus points, and a special part of the contest, you should endeavor to include Sei wearing his favorite jacket (Iseiah's Jacket). If you do not have the items, please click the small teaser image above for the full item in the colors I'd like it drawn in.