I'm pasting some information I found on a Knowledge Base from NI's website. This may help you out. It discusses making the border invisible and how you can do that:
Problem: I am trying to make the border of my cluster container invisible on a front panel in LabVIEW. I have selected the paint brush from the Tools Palette and right-clicked on the border. If I select transparent, nothing seems to happen. What am I doing wrong?
Solution: In order to make the border transparent, you have to change the foreground color to be transparent. By default, when you right-click on the border, it gives you the option to select the background color. However, merely changing the background color will have no effect on the border. To change the foreground color, you
have to right-click on the border, hit the space bar to toggle between the foreground and background, and select the "T" for transparent.
Note: Pressing the space bar once will select both the foreground and background colors. Pressing it twice will toggle to the foreground color alone. A third time will return you to the background color.
You might also assume that selecting the foreground color from the Tools Palette would have the same effect, but by default, the border foreground color cannot be changed by left-clicking on a 3-D control. Therefore, you have to use the method described above to change the transparency of the border. For the cluster container found in Controls Palette » Classic Controls » Array & Cluster, left-clicking will allow you to change the foreground color.
J.R. Allen