In the original Gold/Silver games for Game Boy Color, shiny Pokemon were first introduced to the public as rare collectible versions that appear 1 in 8192 wild encounters.
But most people don't know this one thing about shiny Pokemon and their colors: the developers didn't manually choose shiny Pokemon colors.
All they did was substitute each Pokemon sprite's colors with another suitable palette, and they simply published whatever came out of the other end of that substitution, rarely applying additional touch-ups. To achieve this, sometimes they passed each pixel of the sprites through bitwise filters or masks, or inverted the colors to their complements. Whatever method was used, the output of such operations was reflected in shiny Pokemon during the first 5 generations. Consequently, there's often a 1:1 match between the colors of shiny forms with their non-shiny counterparts.
(Since Bulbasaur doesn't have a pink flower that's bloomed yet, its shiny form also lacks a golden flower.)
This process set a precedent for how shiny Pokemon were "supposed" to look like. Since then, Pokemon has made some modifications, but many species present in much the same form as they did in their original forms from 2000.