Each section of a beam ought to have a different Zadd value. Zadd refers to Z-axis addition. Essentially, Zadd causes the section of the beam in question to be rendered "nearer" to the player, and thus on top of the sections with lower zadds.
The BFGreen, for example, has its widest section, the big green part, with the lowest Zadd value, and each successively narrower layer of the beam at a higher Zadd so that they are "stacked" on top of one another. If the big green section had the highest Zadd value, it would cover over the rest of the sections, and look bad.