Bicycle color, grass color and sky color are all part of the prompt.

>Cartoon illustration of a white pelican wearing a red scarf, riding a red bicycle along a gray road with white dashed lines; the pelican has a large orange beak and webbed orange feet pedaling, with white motion lines behind it; the background shows a light blue sky with white clouds, a yellow sun, two small black birds in flight, and green grass with tiny white flowers in the foreground

That wasn't the prompt. That text was generated by asking the model to describe an image and feeding it a rendering of the SVG it had previously generated.

No, the prompt I always use is "Generate an SVG of a pelican riding a bicycle".