Niddah Color Chart -

Many poskim today provide printed or digital color strips. The process is simple:

The Niddah Color Chart is an essential tool in the observance of Family Purity laws, serving as a visual guide to distinguish between prohibited blood colors and permissible discharges. While modern printed charts provide a useful reference, they are not infallible. The complexity of color perception and the severity of the Halachic implications mandate that ambiguous colors be evaluated by a trained Halachic authority rather than relying solely on self-assessment via a chart. niddah color chart

Default to chumra (stringency) if it’s ambiguous, but ask a rabbi. Many shades of brown are considered tahor unless they clearly tend toward red. Many poskim today provide printed or digital color strips