Red soils and sediments are common in arid and semiarid areas. The red color, caused by iron oxides, has been used by researchers to infer information about sediment provenance, age, and environmental history. However, the objective description and quantification of color is problematic. This paper tests a rapid technique for quantifying redness in the field using visible reflectance spectrometry. The reflectance ratings obtained from the field are converted to redness values and are compared with similar measurements taken under controlled conditions. The results show that the color of dune sands is determined by the variation in intensity of the UV conduction band. We demonstrate that estimates of spectral redness offer much greater precision in differentiating sand samples by color than conventional estimates based on color charts. The relationship between increasing redness and increasing concentrations of iron oxide in the sediments is strong and positive. This suggests that, in certain circumstances, simple field spectral measurements are able to provide reliable estimates of iron oxide concentrations and redness, therefore negating the need for more detailed controlled laboratory measurements.