
Mica blanks most likely will need the tube painted. If you don't, the brass tube will show through the blank.
In some cases, you can mix the mica to make different color variations. Below are some blanks that were made with mica powder.
Another type of powdered pigment that give similar effects to mica is Jacquard Products Pearl Ex. (http://www.jacquardproducts.com/pearl-ex-pigments.html)
Links:
http://theconservatorie.com/
http://www.coastalscents.com/
http://www.jacquardproducts.com/pearl-ex-pigments.html