We compare the mid infrared colors of early type galaxies with isochrones t
hat suitably account for the effects of dust in the circumstellar envelopes
of AGB stars. We show that these stars affect significantly the integrated
colors in the ISO bands. The excess at 10 mum observed in some early type
galaxies combined with the optical spectrum, is compatible with a 100% old
metal rich population. Limits on the additional young components are: age 0
.2 Gyr, mass=0.5% and E(B-V)greater than or equal to0.5 or age 3 Gyr, mass
10% and E(B-V)greater than or equal to0.2.