Exported animated GIFs have 'muddy' colors.

I use Animate to create animated social media posts.

Then I select "File", then "Export", then "Export Animated GIF..."

Sometimes, not always, the colors in the gif are muddy: yellow comes out as dull brown, blue comes as dull green.

I've tried different things, pulling out complex objects, gradients, etc. but I can't figure it out.

Doesn't happen all the time but it can ruin several hours work.

Thank you!