To change the order of the legend without changing the colors of the chart in ggplot2

Question

I am mounting this graphic using the ggplot2 package and prefer it with more neutral colors as in the first image (without vibrant colors), but when I modify the order of the caption the colors of the graphic are modified as well, moving to those of the second image.

"Scale for 'Fill' is already present. Adding Another Scale for 'Fill', which will replace the existing Scale."

This is the return when I try to add the command to change the order of the legend when I already have the colors I want set.

Follow the script without the code to change the order of the legend:

ggplot(data=dfDNA, aes(x=Spp, y=Prop, fill=Elementos)) + geom_bar(stat="identity") + scale_fill_brewer(palette="Dark2") + xlab("Espécies")+ylab("Proproção") + guides(fill=guide_legend(title="Elementos Repetitivos"))

Follow the command to change the order of subtitles:

+ scale_fill_discrete(breaks=c("Gypsy", "Copia", "LINE", "SINE", "Transposons", "DNA Satélite", "Sem Classificação"))

Answer 1

To change the order of the legend, simply change the order of the variable levels fill in scale_fill_brewer with the argument breaks.
Below is an example with the base mtcars. The chart on the left has the legend in the usual order, the chart on the right changes the items 4 and 8.

library(ggplot2)
library(gridExtra)

data(mtcars)

g1 <- ggplot(data = mtcars, aes(x = vs, y = carb, fill = factor(carb))) + 
  geom_bar(stat = "identity") + 
  scale_fill_brewer(palette = "Dark2") + 
  guides(fill = guide_legend(title = "Por ordem"))

g2 <- ggplot(data = mtcars, aes(x = vs, y = carb, fill = factor(carb))) + 
  geom_bar(stat = "identity") + 
  scale_fill_brewer(palette = "Dark2", breaks = c(1:3, 8, 6, 4)) + 
  guides(fill = guide_legend(title = "Trocar 4 e 8"))


grid.arrange(g1, g2, ncol = 2)