  An analytical model has been developed to empirically study the effects of
stellar spots and faculae on the observed equivalent widths of Li {\sc i} 6708,
Na {\sc i} 5896 and K {\sc i} 7699 \AA lines (and abundances in the case of
lithium) in late-type stars, taking into account the changes in the observed
magnitudes and colors. Solar spectra corresponding to different active regions
are used as input data and a range of filling factors are applied to simulate
the surfaces of stars with different levels of activity. Detailed comparisons
between predicted and observed photometric colors and equivalent widths are
made for late-type stars of the Pleiades and the field. The observed
dispersions in K {\sc i} and Li {\sc i} equivalent widths for Pleiades stars
can be partially accounted by the simultaneous effects of activity on colors
and the line formation, indicating that the lithium-rotation connection
suggested for ~0.7-0.9 Msun Pleiades stars could be due in part to the stellar
activity. However, under realistic values for the filling factors, only a small
portion of the observed spread could be explained by these effects
