Dr Rollo mentions that eating rhubarb for 4 days straight results in a yellow color in the blood. Rhubarb is packed with oxalate.
December 4, 1798
Cases of the Diabetes Mellitus
Cases of the Diabetes Mellitus: With the Results of the Trials of Certain Acids, and Other Substances, in the Cure of the Lues Venerea
W. Rhubarb was given, by Doctor Wittman, to a patient for four days; a portion of blood was then taken from the arm, and the serum was, as well as the urine, evidently tinged with its yellow
colour, staining linen.