Passing labels to selectize and returning values for server functions

I want to pass distinct labels to selectizeInput in Shiny. I then want the user input from selectize to pass an encoded parameter value to a function. I have the parameter codes and labels stored in a data frame. So, I should be able to access the parameter field in the data frame using a logical matching statement on the labels. However, I only seem to get the row number as output - not the actual parameter code. Also, multiple selections are not displaying.

Please see example below:

library(shiny)
library(dplyr)

dropdown_A<-as.data.frame( cbind(labels = c("red", "white", "blue"), parameter = c(800, 72, 9048)))
dropdown_B<-as.data.frame( cbind(labels = c("green", "purple", "orange"), parameter = c("xyz","def","abc")))

shinyApp(
  ui = fluidPage(
    fluidRow(
      wellPanel(
        selectizeInput("A", label = p("Select a color"), choices = as.character(dropdown_A$labels), multiple = TRUE),
        selectizeInput("B", label = p("Select another color"), choices = as.character(dropdown_B$labels), multiple = TRUE))),
    fluidRow(verbatimTextOutput("Value_A")),
    fluidRow(verbatimTextOutput("Value_B"))),
  server = function(input, output, session){
    A<-reactive({ 
      if (is.null(input$A))
        return ("Please select a color")
      else (dropdown_A %>% filter(labels == input$A)%>% select(parameter))
    })   
    B<-reactive({ 
      if (is.null(input$B))
        return ("Please select another color")
      else (dropdown_B %>% filter(labels == input$B)%>% select(parameter))
    })  
    output$Value_A<-renderText({
      as.character(A())
    })
    output$Value_B<-renderText({
      as.character(B())
    })
  }
)