How to set colours for groups of elements on a plot

I would like to plot the solution for a differential equation, but have certain solutions a specific colour
I am using Plot.jl and it currently looks like this

I would like to specify that u1(t) to u2(t) are brown, u3(t) to u17(t) are green, and u18(t) to u42(t) are red.

This seems like there should be a simple solution but I cannot find anything in the Plot.jl manual.

Attributes http://docs.juliaplots.org/latest/attributes/ will help.

When drawing the series, set linecolor to a vector of the colors you want.

e.g. plot(rand(100,2), linecolor=[:red, :blue])