ImageMagick: why resized GIF image seems to have some colors replaced by white?

Question

Was wondering if anyone knows what might be causing this.

Original image:

Thumbnail code (using http://aheckmann.github.io/gm/):

  const generateThumb = () => gm(this.getReadStream())
    .in('-thumbnail', '400x400^')
    .in('-gravity', 'center')
    .in('-extent', '400x400')
    .in('+profile', '*')
    .autoOrient()
    .stream()

Resulting image:

Answer 1

Adding -background transparent fixed the problem.