Objective: Hypercholesterolemia (increased blood cholesterol level) is considered a major risk factor for developing atherosclerotic diseases. As such, alerting individuals on hypercholesterolemic conditions is a crucial component in averting onset of atherosclerosis and its outcome—cardiovascular diseases. While common diagnostic tools such as cholesterol and lipoproteins determination are widely employed for hypercholesterolemia screening, their effectiveness has been questioned since they do not shed light on critical physiological factors like lipid oxidation and inflammation levels, which constitute prominent determinants for development of atherosclerotic diseases. The objective of this study is to develop a simple assay for identifying hypercholesterolemia, and assessing the impact of therapeutic treatments. Methods: We developed a diagnostic assay based upon color transformations of polydiacetylene, a unique conjugated polymer, upon interactions with blood plasma obtained from healthy individuals, hypercholesterolemic patients, hypercholesterolemic patients treated with statin, and hypercholesterolemic patients treated with statin together with pomegranate extracts. The color transformations of the polymer were monitored through desktop color scanning combined with colorimetric image analysis. Results: We show that the colorimetric assay was able to distinguish among plasma. Bio-analytical characterization reveals that the distinct colorimetric responses likely arise from interactions with plasma lipoproteins. Importantly, the colorimetric changes are not simply correlated with the relative abundance of cholesterol (or other lipids) in the plasma of hypercholesterolemic or healthy patients, but also reflect the presence of oxidized and inflamed species. Conclusions: This paper introduces a simple color assay for detection of hypercholesterolemia and monitoring the effect of therapies directed at mitigating this physiological condition. The colorimetric system might constitute a novel platform for assessing patient vulnerability towards the development of atherosclerosis.