  We present results of a multi-filter monitoring campaign for very low mass
(VLM) stars in the Pleiades. Simultaneous to our I-band time series (Scholz &
Eisloeffel 2004), which delivered photometric periods for nine VLM stars, we
obtained light curves in the J- and H-band. One VLM star with M~0.15 Ms
(BPL129) shows a period in all three wavelength bands. The amplitudes in I, J,
and H are 0.035, 0.035, and 0.032 mag. These values are compared to
simulations, in which we compute the photometric amplitude as a function of
spot temperature and filling factor. The best agreement between observations
and models is found for cool spots with a temperature contrast of 18-31% and a
very low surface filling factor of 4-5%. We suggest that compared to more
massive stars VLM objects may have either very few spots or a rather symmetric
spot distribution. This difference might be explained with a change from a
shell to a distributed dynamo in the VLM regime.
