A dark red stain was spreading across his shirt.

一个暗红色的污渍正在他的衬衫上渗开。

《柯林斯英汉双解大词典》

The soft red stain is bacterial plaque.

这种暗红色的染色是菌斑。

youdao

Congo red stain will demonstrate the pink material to be amyloid.

刚果红染色淀粉样物呈粉红色。

youdao

But when she turned pale, there was the mark, like a red stain upon snow.

VOA: special.2009.09.26

"First, modern maize pollen grains are larger and turn red when stain is applied, whereas ancient grains do not, " they said.

BBC: Maize was key in early Andean civilisation, study shows

The shavings were then immunostained bathed in a special reagent that would mark the presence of abnormal proteins with a bright, telltale red or brown stain on the surface of the tissue.

NEWYORKER: Offensive Play