Welcome to the site Steve. You will find a ton of info about casting your own blanks as well as working with acrylics which can be a challenge at times for not all plastics are acrylics. Which you will find out. Also looking at your display of pens you probably found out right away that some acrylics are very translucent and the tubes will show through. This happens alot with pen making because we turn down the material quite thin when making blanks. What may look like opaque blank can quickly become translucent. It is highly recommended to do what is known as reverse painting the blank which means paint the inside of the hole of the blank after you drilled it. Some people take other steps to hide tube such as add a drop of paint to the glue used to adhere tube in blank and also paint the tube. To me that is over kill but to each their own. Good luck.