Time series chloropleth in R Shiny / Leaflet

Question

How do you animate a choropleth in RShiny over time using leaflet? I would like to animate the color of choropleths over time in Shiny according to their numeric value.

Below is what I have tried, but the choropleths don't change color after hitting the play button on the slider (or changing the date on the slider). I would like for the choropleths to change color with year as the input.

Here is a link to example that I am looking to replicate, but I cannot seem to get it to work on my end: https://towardsdatascience.com/eye-catching-animated-maps-in-r-a-simple-introduction-3559d8c33be1

Here is the shiny app code:

library(shiny)

library(shiny)

ui <- fluidPage(
  titlePanel("Chamonix Snow Development"),
  
  sidebarPanel(width = 2,
               
               sliderInput("dateSel", "Date",
                           min = min(snow_total_year_abs$year),
                           max = max(snow_total_year_abs$year),
                           value = min(snow_total_year_abs$year),
                           step = 1,
                           timeFormat = "%d %b %y",
                           animate = animationOptions(interval = 200, loop = FALSE)
               )
               
  ),
  
  mainPanel(width = 10,
            
            leafletOutput("map", width = "70%", height = "750px")
            
  )
)


server <- function(input, output, session) {
  
  output$map = renderLeaflet({
    leaflet(stations %>% filter(year==min(stations$year))) %>%
      addTiles() %>% addPolygons( data = vcrop,
                                  weight=2, opacity = 1,
                                  color = stations$color,
                                  fillOpacity = 0.5) 
    
  })
  
  observe({
    leafletProxy({
      leafletProxy("map", data = stations %>% filter(year==input$dateSel)) 
    })
    
  })
  
}

shinyApp(ui, server)

Here is the code getting the coordinate data into polygon form:

test = ac_ml_join %>% filter(Name=="Admont" | Name =="Fieberbrunn")

stations = st_as_sf(test,coords = c("Longitude","Latitude"))

#create voronoi/thiessen polygons
v <- stations %>% 
  st_union() %>%
  st_voronoi() %>%
  st_collection_extract()

box <- st_bbox( stations ) %>% st_as_sfc()
vparts = st_collection_extract(v)
vcrop = st_crop(vparts, box)

leaflet(stations) %>% 
  addTiles() %>% 
  #addCircleMarkers( data = stations ) %>%
  addPolygons( data = vcrop,fillColor = stations$color,
               weight=2, opacity = 1,
               color = stations$color,
               fillOpacity = 0.5) 

'Test' dataset:
year max.snow Name    `3yr_roll_avg` snow.vis color     Longitude Latitude
1971    4.35  Absdorf          2.93     100   royalblue      16.0     48.4
1972    2.28  Absdorf          3.07     105.  royalblue      16.0     48.4
1973    2.58  Absdorf          1.62      55.2 red            16.0     48.4
1974    0     Absdorf          1.16      39.6 darkred        16.0     48.4
1975    0.903 Absdorf          0.508     17.3 darkred        16.0     48.4
1976    0.621 Absdorf          3.31     113.  royalblue      16.0     48.4
1977    8.42  Absdorf          5.44     186.  purple         16.0     48.4
1978    7.29  Absdorf          8.04     274.  purple         16.0     48.4
1979    8.42  Absdorf          7.41     253.  purple         16.0     48.4
1980    6.52  Absdorf          6.02     205.  purple         16.0     48.4
1971     20.9 Admont           8.77     100  royalblue      14.5     47.6
1972      3.6 Admont          26.4      301. purple         14.5     47.6
1973     54.7 Admont          29.7      339. purple         14.5     47.6
1974     30.9 Admont          42.8      488. darkred        14.5     47.6
1975     42.9 Admont          39.6      451. purple         14.5     47.6
1976     45.0 Admont          43.2      492. purple         14.5     47.6
1977     41.7 Admont          42.5      485. red            14.5     47.6
1978     40.9 Admont          37.3      426. purple         14.5     47.6
1979     29.4 Admont          40.7      464. purple         14.5     47.6
1980     51.8 Admont          56.8      647. purple         14.5     47.6