I don’t know what it is, but I’m a total sucker for pretty pens.
And these Paper Mate InkJoy 300 RT Retractable Medium Point Ballpoint Pens, Assorted Colors, 8 Pack (1781564) are some of my favorite. They are awesome for color-coding a calendar (one color per family member) — or just about anything.
Amazon has them the 8-pack for just $2.78, regularly $4-$7 in the office supply stores.
Note that these are an Add-On item, which means they ship for free when you have a total of $25 worth of items in your cart. This item does count toward that total.
Amazon pricing can change on a dime, so please confirm prices before you check-out.