switching between color and grayscale

I am mildly concerned about how my plots will look if someone prints
my thesis out in grayscale. Is there an easy way to use the same code
with one switch at the beginning to plot in color or grayscale? Is
there a way to redefine what happens when I call plot(x,y,'g-') so
that 'g-' no longer means green but now means something like
color=0.75 so some grayscale specification?

Does anyone have a suggestion for line types that work well in grayscale?