Shiny finally has a colour picker – use colourInput to select colours in Shiny apps

I don’t always think Shiny is missing anything, but when I do – I fill in the gap myself.

That was meant to be read as The Most Interesting Man In The World, but now that I think about it – maybe he’s not the type of guy who would be building Shiny R packages…

Shiny has many useful input controls, but there was one that was always missing until today – a colour picker. The package shinyjs now has a colourInput() function and, of course, a corresponding updateColourInput(). There have been many times when I wanted to allow users in a Shiny app to select a colour, and I’ve seen that feature being requested multiple times on different online boards, so I decided to make my own such input control.

Table of contents

• Demo
• Availability
• Features
  • Simple and familiar
  • Allowing “transparent”
  • How the chosen colour is shown inside the input
  • Updating a colourInput
  • Flexible colour specification
  • Works on any device
• Misc

Demo

Click here for a Shiny app showing several demos of colourInput. If you don’t want to check out the Shiny app, here is a short GIF demonstrating the most basic functionality of colourInput.

The colours of course don’t look as ugly as in the GIF, here’s a screenshot of what a plain colourInput looks like.

Availability

colourInput() is available in shinyjs. You can either install it from GitHub with devtools::install_github("daattali/shinyjs") or from CRAN with install.packages("shinyjs").

Features

Simple and familiar

Using colourInput is extremely trivial if you’ve used Shiny, and it’s as easy to use as any other input control. It was implemented to very closely mimic all other Shiny inputs so that using it will feel very familiar. You can add a simple colour input to your Shiny app with colourInput("col", "Select colour", value = "red"). The return value from a colourInput is an uppercase HEX colour, so in the previous example the value of input$col would be #FF0000 (#FF0000 is the HEX value of the colour red). The default value at initialization is white (#FFFFFF).

Allowing “transparent”

Since most functions in R that accept colours can also accept the value “transparent”, colourInput has an option to allow selecting the “transparent” colour. By default, only real colours can be selected, so you need to use the allowTransparent = TRUE parameter. When this feature is turned on, a checkbox appears inside the input box.

If the user checks the checkbox for “transparent”, then the colour input is grayed out and the returned value of the input is transparent. This is the only case when the value returned from a colourInput is not a HEX value. When the checkbox is unchecked, the value of the input will be the last selected colour prior to selecting “transparent”.

By default, the text of the checkbox reads “Transparent”, but you can change that with the transparentText parameter. For example, it might be more clear to a user to use the word “None” instead of “Transparent”. Note that even if you change the checkbox text, the return value will still be transparent since that’s the actual colour name in R.

This is what a colour input with transparency enabled looks like

How the chosen colour is shown inside the input

By default, the colour input’s background will match the selected colour and the text inside the input field will be the colour’s HEX value. If that’s too much for you, you can customize the input with the showColour parameter to either only show the text or only show the background colour.

Here is what a colour input with each of the possible values for showColour looks like

Updating a colourInput

As with all other Shiny inputs, colourInput can be updated with the updateColourInput function. Any parameter that can be used in colourInput can be used in updateColourInput. This means that you can start with a basic colour input such as colourInput("col", "Select colour") and completely redesign it with

updateColourInput(session, "col", label = "COLOUR:", value = "orange",
  showColour = "background", allowTransparent = TRUE, transparentText = "None")

Flexible colour specification

Specifying a colour to the colour input is made very flexible to allow for easier use. When giving a colour as the value parameter of either colourInput or updateColourInput, there are a few ways to specify a colour:

• Using a name of an R colour, such as red, gold, blue3, or any other name that R supports (for a full list of R colours, type colours())
• If transparency is allowed in the colourInput, the value transparent (lowercase) can be used. This will update the UI to check the checkbox.
• Using a 6-character HEX value, either with or without the leading #. For example, initializing a colourInput with any of the following values will all result in the colour red: ff0000, FF0000, #ff0000.
• Using a 3-character HEX value, either with or without the leading #. These values will be converted to full HEX values by automatically doubling every character. For example, all the following values would result in the same colour: 1ac, #1Ac, 11aacc.

Works on any device

If you’re worried that maybe someone viewing your Shiny app on a phone won’t be able to use this input properly – don’t you worry. I haven’t quite checked every single device out there, but I did spend extra time making sure the colour selection JavaScript works in most devices I could think of. colourInput will work fine in Shiny apps that are viewed on Android cell phones, iPhones, iPads, and even Internet Explorer 8+.

Misc

In order to build colourInput, I needed to use a JavaScript colour picker library. After experimenting with many different colour pickers, I decided to use this popular jQuery colour picker as a base, and extend it myself to make it geared to work with Shiny. I simplified much of the code and added some features that would make it integrate with Shiny much easier. You can see the exact changes I’ve made in the README for my version of the library. The main features I added were the support for a “transparent” checkbox, the complete look of the input field was redesigned, and I also changed the colour picker colours to render completely in CSS instead of using images.

It’s been pointed out that this function is not exactly in-line with the general shinyjs idea, so it might not stay there forever. Ideally, this colourInput will soon be part of shiny, but until then I’ll just keep it here until it finds a more loving home.

If anyone has any comments or feedback, both negative or positive, I’d love to hear about it! Feel free to open issues on GitHb if there are any problems.