ggplot points have color but legend (guide) points are all black

Question

I have a ggplot where I want to fill points with color based on ID and set shapes based on Group, using shapes 21 and 22, which have an outline color and a 'fill' color. The points in the plot are correct, but the legend or guide on the right has all points shown as black.

Here's a code example:

library(ggplot2)

data <- list()
data[['ID']] <- c("1","1","1","1","2","2","2","2","3","3","3","3")
data[['Group']] <- rep(c("A","B"),6)
data[['x']] <- seq(1:12)
data[['y']] <- log(data[['x']])

df <- data.frame(data)
df

# I want to use point shapes with outlines (shapes 21,22, and 23) assigned 
# to different 'Group' (A or B), outline is set at black.
# Colors are manual filled as red, blue and green based on 'ID' ("1", "2", or "3")
# The problem is the ggplot guide for Color is all black. 
# The guide/legend doesn't reflect the point fill color based on ID.
ggplot(df, aes(x=x, y=y, fill=ID)) + 
  geom_point(aes(shape=Group, fill=ID), size=6) +
  scale_fill_manual(values = c("1"="red", "2"="blue", "3"="green")) + 
  scale_shape_manual(values=c("A"=21,"B"=22))

`

My expectation is that the legend will reflect the point colors. Ggplot shapes 21 and 21 have a fill attribute (can be filled). That means scale_fill_manual is the correct option. I've tried combinations of fill and color at the ggplot level, geom_point call (in aes), but I haven't been able to find the combination that will work. It seems like the legend is taking its color from the outline of the shapes, black (default) in this case.

Answer 1

guides(fill = guide_legend(override.aes = list(shape=21)))

The issue is that the legend for fill does not "know" that you are using non-default shapes for your points, so we can override the default to make it use shape 21. The various shapes treat color, fill, and stroke aesthetics differently.