Texture learning

Hi, new around here and with blender and I’m trying yo figure out a lot of things but there is something that seems difficult and is about textures and how to handle them.

I’m making this scene that is mostly to figure out materials and lights
the final result is a composition of 2 scenes one is a volumetric light that is the ray of the left and the prism with the lights inside.

I’m trying to fake the refraction of the rainbow going out of the prism and the fusion of the inside lights also I’m not sure why the volumetric light don’t get inside the prism even giving it enough distance to cross the scene.

The lights inside the prism are actually 2 trapezoids with glass materials and set to emission and the rainbow one have that texture in the “hidden” face only, well if I extrude that trapezoid and give it the shape of the refraction the rainbow
don’t behave like it should the colors just expand and there is only blue and green colors along the shape, how should I edit the texture to keep the rainbow shape even if I expand the mesh?

How do I should fake the transition from white light to visible spectrum?

Thanks and excuse my English.

Solved, just had to set the stretching of the texture.