This one is just fun! While playing around with a more complex color mix I had leftover yellow and bright pink and put them together... The result was so nice I had to add it to the lineup. After drilling you can back paint this one white to lighten the colors or a neutral silver or even yellow would work. It's pretty opaque so would only be an issue on pens with extremely thin walls.
Slim Blanks measure about .6" x 5" and are suitable for slimlines and pretty much any pen around .5" finished diameter. Drilling on the lathe is your best bet to ensure you maximize the diameter.