Shiny Bulbasaur doesn't have a golden bulb but Ivysaur and Venusaur do Shiny Bulbasaur doesn't have a golden/shiny bulb but Ivysaur and Venusaur do. Was that intentional, or did they realize that they should make the bulb shiny when they started drawing Ivysaur or Venusaur?





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Bulb  Bulbs are golden
isn't
golden
It's the seed on shiny Ivysaur and Venusaur that is golden. While still a Bulbasaur, the bulb as yet to bloom and the seed is covered by the green leaves.

In one episode of the anime, it shows a Bulbasaur evolve into an Ivysaur. Albeit it's not shiny, you can clearly see the evolution process causes the bulb to bloom which reveals the seed on its back.