geom_smooth: transparency of the smooth fitting line

[Breeze-Hu]

The current parameter ’alpha‘ of geom_smooth is used to adjust the color transparency of the confidence intervals. Would it be interesting for the authors to provide a simple parameter for the transparency of the fitted line to adjust? Although the color of the current fitted line can be precisely adjusted (HEX values).

Or is it due to my negligence that I haven't found the relevant parameters yet? Please remind me, thanks!

[clauswilke]

You can use RGBA colors to draw transparent fitted lines.

[teunbrand]

In addition, you can use after_scale() to modify any pre-existing colour.

library(ggplot2)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  geom_smooth(
    aes(colour = after_scale(alpha(colour, 0.3)))
  )
#> `geom_smooth()` using method = 'loess' and formula = 'y ~ x'

^{Created on 2024-10-02 with reprex v2.1.1}

[Breeze-Hu]

You can use RGBA colors to draw transparent fitted lines.

Thank you for your reply! This is indeed a solution to the problem.

[Breeze-Hu]

In addition, you can use after_scale() to modify any pre-existing colour.

library(ggplot2)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  geom_smooth(
    aes(colour = after_scale(alpha(colour, 0.3)))
  )
#> `geom_smooth()` using method = 'loess' and formula = 'y ~ x'

Created on 2024-10-02 with reprex v2.1.1

Thank you! That would be the perfect answer!
Thank you very much for your prompt reply!

[Breeze-Hu]

In addition, you can use after_scale() to modify any pre-existing colour.

library(ggplot2)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  geom_smooth(
    aes(colour = after_scale(alpha(colour, 0.3)))
  )
#> `geom_smooth()` using method = 'loess' and formula = 'y ~ x'

Created on 2024-10-02 with reprex v2.1.1

Dear developer, I've encountered another issue while testing.
When used with facet_wrap, the colors are out of expectation.
There are supposed to be three colors, but now there is only blue, and also the legend is faulty.

ggplot(iris,aes(x = Sepal.Length, y = Sepal.Width,colour = Species))+
geom_point()+
geom_smooth(method = 'lm',fullrange = TRUE,
aes(colour = after_scale(alpha(colour, 0.3))))+
facet_wrap(~Species,nrow = 2)

[teunbrand]

You can use colour = stage(Species, after_scale = alpha(colour, 0.3)) in your smooth layer if you both want to map a variable and adjust its alpha.

[Breeze-Hu]

Perfect! Thank you very much.

I have one more question for you and I hope you can give some advice.

For example, I would like to change the color of the x-axis annotation to have multiple colors at the same time (which is really rare). But it will indicate that there is a problem:
“Warning message:
Vectorized input to element_text() is not officially supported.
ℹ Results may be unexpected or may change in future versions of ggplot2. ”

ggplot(iris,aes(x = Sepal.Length, y = Sepal.Width,colour = Species))+
geom_point()+
geom_smooth(method = 'lm',fullrange = TRUE,
aes(colour = stage(Species, after_scale= alpha(colour, 0.3))))+
facet_wrap(~Species,nrow = 2)+
theme(legend.position = 'inside',
legend.position.inside = c(0.75,0.25),
axis.text.x = element_text(color = c(rep('red',2), rep('blue',2)))
)

I hope you understand that this is not unreasonable, but is intended to achieve an effect similar to the one below:

[teunbrand]

This is unrelated to the original issue and for help we generally redirect you from the issue tracker to stack overflow or the Posit community. I'll close this issue, as this has generally been a line of inquiry rather than a bug report or feature request.
That said, the {ggtext} and {marquee} packages offer options to recolour text.

[Breeze-Hu]

Thank you! Solved the problem perfectly!