Oh yep if you’re losing the texture is because on AlphaComposite materials the setup is a bit different and you need to multiply the opacity to the emissive color of the material, here’s a post from a while back from someone also explaining how the blend mode works if it helps!
Even though the alpha composite can help, you also need to take into account that the color of the background influence translucent materials, even if they’re additive or alphacomposite, so I don’t think your issue is with the lighting affecting the color but rather that a red color against the yellow bright of the sand is not going to work as well as against a darker background like in the shadow. You can also see that on the documentation of the post I linked.
I would try adding a second laser in your Niagara system that is rendered behind the one you have and is a dark red and less defined so that it works sort of like a background to your main laser and helps creating more color contrast, sort of like this:
Hope it helps!