Color predictions. From left to right, each panel shows the color sensitivity of the photometric and spectroscopic FASTAR models (dashed and solid blue lines, respectively), as well as the MILES predictions (in orange) for comparison. The differences between the three models are due to the use of theoretical versus empirical stellar libraries and the choice of bolometric corrections (between FASTAR and MILES). The assumed ages, metallicities and IMF slopes are the same as in Fig. 6.