I’m not aware of a general recipe in Plots to create a vector of colors. As Rafael pointed out, if you have more than three states, the vector of colors will not be linearly independent. As a consequence, there is not a unique mapping between color and underlying probability distribution. However, if you have three states, Rafael’s code below will have a unique mapping. His code is equivalent to colors = [RGB(1,0,0), RGB(0,1,0), RGB(0,0,1)]. This works out nicely because the implied basis is orthogonal and linearly independent.
plot(t, y, c=RGB.(eachcol(probs)...), lw=3, leg=false)
plot!(t, probs, c=[:red :green :blue])