1.
a touch of anxiety; a slight unease; a lingering worry
A faint but persistent feeling of worry or concern. The word 一抹 means "a trace" or "a touch," so the expression conveys a small but nagging sense of unease.
Usage
一抹 literally means "one stroke" (of a brush), evoking the image of a thin, faint line. The expression is semi-literary and often appears in written Japanese, news articles, and formal speech. It conveys worry that is small but cannot be dismissed.