Create a dynamic dataframe based on bar clicked in plot

I am trying to run the code below to filter a dataframe based on the selection made in the plot.
When I replace filter(category()==1 with English==1 or Math==1, it works fine, but i would like to use it dynamically based on the selection made in the Bar plot.

Also, how can i make the bar selected a different color? Like when English is selected, I would like to show it as Blue and other bars faded.

library(shinydashboard)
library(shiny)
library(dplyr)
library(ggplot2)
library(tidyr)
library(plotly)

subject <- c('Math','Science','English')
TotStudents <- c(13, 15, 20)

sub_freq <- data.frame(subject, TotStudents)
sub_freq

name <- c('Sam', 'John', 'David', 'Bill', 'Jack', 'Peter', 'Zach')
Math <- c(1,0, 1, 1, 0, 1, 1)
Science <-c(0,0, 1, 1, 1, 0, 1)
English <-c(1,1, 0, 1, 0, 1, 0)

name_flag <- data.frame(name, Math, Science, English)
name_flag

ui <- dashboardPage(
dashboardHeader(title = "Test Dashboard",titleWidth = 200),
dashboardSidebar(
),
dashboardBody(
plotlyOutput("cond", height = "500px", width="600px"),
br(),
uiOutput("imageLink"),
br(),
DTOutput("datatable")

)
)

server <- function(input, output) {

category <- reactiveVal()

observeEvent(event_data("plotly_click", source = "imgLink"), {
category(event_data("plotly_click", source = "imgLink")$x)
})

Create text paragraph of info on a selected point

output$imageLink <- renderText({
event.data <- event_data(event = "plotly_click", source = "imgLink")
if (is.null(event.data)) {
print("You can click on a bar to select a subject.")
} else {
category()
}
})

output$cond <- renderPlotly({
event.data <- event_data(event = "plotly_selected", source = "imgLink")

sub_freq %>%
  plot_ly(x = ~subject, y = ~TotStudents, source = "imgLink") %>%
  layout(title = "Student Count by Subject")

})

output$datatable<- renderDataTable({
name_flag
mbrs <- name_flag %>%
filter(category()==1)

})

}

shinyApp(ui, server)