Thirty species of the glassfrogs genus Nymphargus, including a new species, are known to inhabit the cloud forest of the Andes of Colombia and Ecuador. Four of these species (Nymphargus anomalus, N. ignotus, N. rosada, and the new species) are unusual by having a tanbrown dorsal coloration instead of the widespread green coloration commonly found in glassfrogs. Herein, we review tan-brown glassfrogs species, providing information on their external morphology, color ontogeny, ecology, and distribution. The new taxon inhabits the Andes of southwestern Colombia, Departamento del Cauca, and it is distinguished from other centrolenids by having a tan-brown dorsum with dark spots lacking ocelli, reduced (basal) webbing between outermost fingers, and lacking iridophores on the digestive tract and hepatic peritonea. We also find that Nymphargus ignotus is a polymorphic species distributed along the western flank of the Cordillera Occidental in Colombia. The egg masses of N. ignotus are similar to those known in others Nymphargus species, except for the presence of supplementary empty capsules. The distribution, abundance and function of empty capsules and the nature of the tan-brown color pattern in glassfrogs are discussed.