PrettyLitter is a proprietary silica gel litter with health diagnostic features. Its litter changes color as a reaction to a cat's urine to indicate potential health issues. The litter turns blue in the presence of high alkaline urine (a potential an indication of a urinary tract infection), yellow for high acidic urine (potentially indicating metabolic acidosis or kidney tubular acidosis), or red in the presence of blood in the urine (which might indicate bladder inflammation, bladder stones, or a urinary tract infection).