If reddish light is used, the meter reads zero, since no electrons are ejected. More reddish light changes nothing: the meter still reads zero. As the frequency is increased and the color changes to be more blue/violet, at some point the energy per photon is sufficient to eject electrons, and the meter will give a nonzero reading. If this light intensity is increased, the meter reading increases because more electrons are ejected.
Work Step by Step
This is explained on pages 585-587.