Taillights have white texture when shining

[Turkish20]

When taillights are turned on, my texture gets white in few areas. What could be the cause of this? Do I have to paint it somehow in Zmodeler? I also tried appealing black background for the light texture as well as turning off diffuse colour but it didn't helped.

[Oleg]

most likely you should paint the surrounding area to black on texture's alpha to dim the light on sides/edges.

[Turkish20]

Somebody else told me, that I should paint the vertices into red. It worked, but I never understood the painting thing and what is it good for.