A single material will save as a single square, as an approximation - similar to Preview Mode - of how the material will look. Poser often can't show complex materials correctly in Preview, so you get these odd results sometimes. If you save a Material Collection, you'll get a thumbnail of the figure it was saved from.

Ironsoul's advice is the best way to go; it's how you'd do it for packaging an item to upload, free or for sale.

Coppula eam se non posit acceptera jocularum.

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