Swarth is a somewhat obscure word, but there are plenty of synonyms that can be used in its place. Some possible options might include dark, dusky, tawny, sable, or ebony. These words all convey a sense of darkness or pigmentation. Other potential synonyms might include somber, gloomy, or shadowy, which evoke a more metaphorical sense of darkness or a lack of light. Depending on the context, other synonyms might also be appropriate, such as indistinct, obscured, or obscured, all of which refer to something being difficult or impossible to see or perceive clearly. Whatever word you choose, it's important to choose one that accurately reflects the intended meaning of the original word.