Opacity/alpha as attribute linked to a continuous variable

I am trying to get a continuous transparency according to a continuous variable that also defines the color. I've tried the code suggested in this post https://github.com/ropensci/plotly/issues/389 but I dont manage to do what I want and, in fact, I get very unexpected plots since the colorbar and marker's colors do not match + transparency seems the same for all colors.

require(plotly)
plot_ly(x = rnorm(100), y = rnorm(100), z = rnorm(100),
color = rbeta(100,shape1=1,shape2=1),alpha=.2,
type = "scatter3d", mode= "markers",
colors=colorRamp(c("blue","red")))

I'd like to get low transparency at high color values and vice versa. Is this possible in the currrent version of plot_ly?

plot_ly(x = rnorm(100), y = rnorm(100), z = rnorm(100),
color = rbeta(100,shape1=1,shape2=1),opacity=.2,
type = "scatter3d", mode= "markers",
colors=colorRamp(c("blue","red")))

setting opacity instead of alpha seems to fix the colouring vs colorbar but not the transparency issue.

Start with the reproducible plot_ly scatter3d examples in the issue and investigate how color, alpha, and opacity are mapped for markers. Verify the behavior against the colorbar and marker appearance; done means a continuous variable can control both color and transparency as requested, without mismatched colors.