Simple Beam temporarily changes the target's ability to Simple. It does not work on Pokémon with the Truant or Multitype ability.
With this effect, the opponent's stat modifiers, both positive and negative, double in effectiveness.~Bulbpidia
In other words that all that happens it says nothing about it increasing a chance for shiny pokemon to appear which was probably a coincidence as nothing can increase the chance for a wild shiny to appear,
As for the black beam ive never heard of that happening if you were playing in the dark you may have seen it wrong and i searched everywhere and cant find anything on it so like i said you probably just miss-saw.