Despite the great developments that have been achieved in the last decade in disentangling most relevant stellar population parameters, in particular with the inclusion of absorption linestrength indices, the age-metallicity degeneracy still lurks in these studies. Here I summarize our effort for developing the stellar population synthesis method, which includes models predicting full spectral energy distributions of stellar populations at moderately high resolution. We show how these model spectral energy distributions open up new possibilities to overcome this degeneracy, such as optimized indices with enhanced sensitivities to age, metallicity, and abundance ratios of various key species. These tools are applied to well-selected samples of early-type galaxies embedded in various environments, allowing us to further our understanding of the origin of the color-magnitude relation and of galaxy formation timescales as a function of cluster properties.