Makie Alpha property in colormap is not observable. What's best way to mech this?

I have a function that makes a plot using lines/lines!. I can pass observables into the function and get the line x,y,z, and colormap value to update dynamically. The alpha value does not update as an observable.

What is the best way to achieve this?

Here is a minimum working example. Which shows alpha not being updated.

using GLMakie
using ColorSchemes


colormap = @lift((:lightrainbow, $alpha))

Thank you. I got near this several times, I think I tried to do the lift in place and messed it up and convinced myself there was something different about alpha.