The particle laser_sight_beam has an odd way of determining its color. Instead of the usual particle settings, the laser's color is determined by the position of its controlPoint2 on the map's coordinates.

It uses an RGB system. controlPoint2's position on the X axis determines the laser's red value. The Y axis determines green. The Z axis determines blue. At the origin, the coordinate 0, 0, 0, the laser has no color, making it invisible.

To make the laser red, you want only a positive X coordinate. 20, 0, 0 works just as well as 255, 0, 0.
Here's the easiest way to get there.

After you've set up the models how you want them, add the particle effect laser_sight_beam under class_fx.pcf


Move the transform onto the laser attached to the right turret, or wherever you want one end. Move controlPoint1 to what the Engineer is aiming at, or wherever you want the other end.
The laser could be any color, depending on what map you're on. Yellow, pink, and teal are common.

Check the box next to controlPoint2 without dragging anything onto it. This will lock it onto the map.



Select controlPoint2 and up the Zero slider all the way. controlPoint2 will zoom off to wherever the Default Point of your map is. This is the coordinate 0,0,0. Use the work camera to look around if you lose sight of it. While controlPoint2 is at 0,0,0, the wrangler laser should be invisible.



Slide controlPoint2 forward along the red X axis to make the laser red.



Slide controlPoint2 up the blue Z axis to make the laser blue.



For other colors, the laser works as a RGB system. Sliding controlPoint2 to the side on the green Y axis makes the laser green. You can slide it up each axis to make it more or less of each color. Going into the negatives is the same as if it were at 0 on that axis.