"More bister" is a phrase that means to become more grayish or colorless. There are several synonyms that relate to this concept. The word "blanched" means to become pale or colorless, while "wan" means appearing pale or sickly. "Ashen" refers to someone whose complexion is grayish, as if they've been exposed to ash or dust. "Hoary" means gray-white in color, while "pallid" refers to an unhealthy, pale appearance. "Drab" describes something that is dull or lacking in color, while "dull" means lacking brightness or vividness. Overall, these synonyms all capture the idea of something becoming more bister or drab.