There is some debate about the status of very light pastels. Our halachic position is to treat light pastels (other than off-white) as a colored surface. Thus, light pink is a colored surface and stains on it without hargashah do not render a woman niddah.
Nevertheless, as a precaution against having relations when a flow begins, we would recommend abstaining from relations for at least twenty-four hours, or until you are sure the staining has ceased.
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