Thanks for trying to help, but this isn't my situation. Let me be more explicit:
gr1=ListPlot@elaborate calculation .... which takes several minutes and I don't want to run it again
gr2=ListPlot@ another elaborate calculation .... which takes several minutes and I don't want to run it again
When I made gr1 and gr2, I didn't plan on showing them together, so I didn't do anything special about the colors. Now I want to put them together, and have gr1 in one color and gr2 in another color. So I want to do something like
Show[
Style[gr1,Red],
Style[gr2,Green]
]
but this doesn't work.