Hydrogen peroxide, baking soda, let dry. Then vinegar on top of that. Don’t mix vinegar and hydrogen peroxide in the same bottle. It creates an unstable form of peracetic acid. Peracetic acid us used in an industrial setting as a disinfectant. Corrosive tho, so not recommend Ed for household.

If all else fails, dye your sheets a nice rich color. Also great for giving life to dingy clothes you’re tired of.