Persistent form modifications of silver nanoparticles in glass and the resulting dichroitic color changes induced by irradiation of a single intense femtosecond laser pulse were studied by means of high-resolution electron microscopy and spatially resolved optical transmission spectroscopy. Electron microscopy reveals a variety of morphological changes of the silver particles, in particular irregularly shaped particles surrounded by halolike structures consisting of very small silver clusters. The spectral analysis suggests that at lower intensities preferably desorption of silver into the glass matrix occurs producing isotropic spectral changes, while at higher intensities anisotropic spectra caused by particle deformation are observed. An analysis of the effects produced by different laser wavelengths allows one to correlate these findings with the variations of particle sizes depending on their penetration depth.