Normal urine colour is due primarily to the presence of waste products from the metabolism of hemoglobin (porphyrin, bilirubin, urobilin, etc.). Depending on how diluted the urine is (see Density), urine can take a colour ranging from very pale yellow to orange or amber. On top of the base colour, different hues are caused by multiple food-related compounds (beets, rhubarb, etc.), medications, or urate crystals. Red or brown urine may indicate the presence of blood or hemoglobin. This possibility is confirmed by using test strips and a microscope to look for blood (see those headings).