R- Shiny -如何更改饼图中图例的颜色？

library(shiny)
library(ggplot2)

# 定义UI
ui <- fluidPage(
  titlePanel("自定义饼图图例颜色"),
  mainPanel(
    plotOutput("pieChart")
  )
)

# 定义服务器逻辑
server <- function(input, output) {
  output$pieChart <- renderPlot({
    # 示例数据
    data <- data.frame(
      category = c("A", "B", "C", "D"),
      value = c(10, 20, 30, 40)
    )
    
    # 创建饼图
    p <- ggplot(data, aes(x = "", y = value, fill = category)) +
      geom_bar(stat = "identity", width = 1) +
      coord_polar("y", start = 0) +
      theme_void() +
      scale_fill_manual(values = c("red", "blue", "green", "purple"))  # 自定义颜色
    
    # 自定义图例
    p + guides(fill = guide_legend(override.aes = list(color = "black")))  # 设置图例颜色为黑色
  })
}

# 运行Shiny应用程序
shinyApp(ui = ui, server = server)