Color Individual Lines with Gadfly

Is there a way to color each dataset?

There is a solution using DataFrames, but what about cases without them?

I tried this, but it has no effect:

using Gadfly

plot(
  layer(x=1:10, y=1:10, Stat.step, Geom.line),
  layer(x=1:10, y=2:11, Stat.step, Geom.line),
  color=["red", "green"]
)