Ok, have another idea. In your script, call these [once] after the level has been loaded.
var fullvector[3] = 255, 255, 255;
vec_set(mat_model.diffuse_blue, fullvector);
vec_set(mat_model.ambient_blue, fullvector);
vec_set(mat_model.specular_blue, nullvector);
vec_set(mat_model.emissive_blue, nullvector);
mat_model.albedo = -100;
This should remove sun lighting. Also try setting sun_light = 0;