I don't know if it is a manhwa, manhua or webtoon. It is full-colored and this is the synopsis:
It's set in a historical, European era with nobles, etc. The female lead is a noble with an over-powered wizard sister. The male lead is a noble of a plagued territory. (It's possible he has black hair.)
The female lead (noble) got into a loveless marriage with the male lead (noble). He isn't home for years because of war and she suffers from her stepmother's abuse.
After her husband comes home, he is even colder. His territory declines more and more until the emperor suddenly accuses the husband of treason.
The husband pleads for the life of his wife because she is pregnant but she still gets killed by the emperor's sword.
She starts at her wedding night again and changes her life.
The first thing she does is get her husband to stay. Afterwards she stops her stepmother from using her money and invests it into the territory. With the knowledge of her previous life, she tries to change the direction of the territory.
She also reconciles with her family a bit, which is how the reader knows why she got married instead of her sister.