[R] adjusting color palette

[Laura Quinn]

Is there a way to increase the "sensitivity" of the color palette in order
to more clearly represent certain sections of data? For example I am
wanting to clearly differentiate between height data for a rolling
landscape but because of the extremes of the dataset (sea and mountain
tops), the bulk of the landscape is shaded in closely approximating green
- i have attempted to do this by using a larger color palette but this
doesn't make things any clearer.
Thanks
Laura