midpoint is not transformed in scale_color_gradient2

[zeehio]

When using scale_color_gradient2 with trans = "log10", I was expecting the midpoint to be transformed as well. The documentation does not specify how midpoint behaves under transformation.

Reproducible example

Without transformation:

library(ggplot2)
df <- data.frame(x = c(1, 10, 100), y = c(1, 10, 100), color = c(1, 10, 100))
color_midpoint <- 10
ggplot(df) +
  geom_point(aes(x = x, y = y, color = color)) +
  scale_color_gradient2(midpoint = color_midpoint, low = "red", mid = "green", high = "blue")

With transformation

ggplot(df) +
  geom_point(aes(x = x, y = y, color = color)) +
  scale_color_gradient2(midpoint = log10(color_midpoint), low = "red", 
                        mid = "green", high = "blue", trans = "log10") +
  coord_trans(x = "log10", y = "log10")

I was expecting to use midpoint = color_midpoint so the trans = "log10" would apply to both the color aesthetic and the midpoint. However I had to apply manually midpoint = log10(color_midpoint).

The main advantage of letting the trans transform the midpoint is that if I change the transformation then the midpoint keeps being valid (and consistent with the aesthetic units), while now I have to manually transform the midpoint for every transformation I use.

Is is possible to change the behaviour of midpoint so it affected by trans? If not, is it possible to document this behaviour?

Thanks for your time and splendid work