This one is a fun mix of rich purple and neon green. Some folks like to call this one "Joker" inspired. The green will fluoresce in black light. Shouldn't need to paint the tube but if you do I'd go with black or maybe a silver as a neutral.
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.