diff --git a/CHANGELOG.md b/CHANGELOG.md
index a407228..d814ea6 100755
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,14 @@
+# 4.1.0 - 2019-04-01
+
+- Added: `preserveCustomProps` option to preserve custom properties
+- Updated: `postcss` to 6.0.23 (patch)
+- Updated: `postcss-value-parser` to 3.3.1 (patch)
+
+# 4.0.1 - 2017-11-03
+
+- Fixed: bug when using the `tint`, `shade`, and `contrast` adjusters along with the `alpha` adjuster
+([#33](https://github.com/postcss/postcss-color-function/pull/33) - @tylergaw)
+
 # 4.0.0 - 2017-05-15
 
 - Added: compatibility with postcss v6.x
@@ -8,7 +19,7 @@
 - Changed: send postcss warning when color function cannot be parsed instead of throwing
 ([#35](https://github.com/postcss/postcss-color-function/pull/35) - @drewbourne)
 - Changed: send a postcss message when color function contains a var()
-([#36](https://github.com/postcss/postcss-color-function/pull/36) - @drewbourne)

+([#36](https://github.com/postcss/postcss-color-function/pull/36) - @drewbourne)
 
 # 2.0.1 - 2016-03-15
 
diff --git a/README.md b/README.md
index 6081353..d0ad387 100755
--- a/README.md
+++ b/README.md
@@ -1,11 +1,21 @@
-# postcss-color-function [![CSS Standard Status](https://jonathantneal.github.io/css-db/badge/css-color-modifying-colors.svg)](https://jonathantneal.github.io/css-db/#css-color-modifying-colors) [![Build Status](https://travis-ci.org/postcss/postcss-color-function.svg)](https://travis-ci.org/postcss/postcss-color-function)
+# postcss-color-function [![Build Status](https://travis-ci.org/postcss/postcss-color-function.svg)](https://travis-ci.org/postcss/postcss-color-function)
 
-> [PostCSS](https://github.com/postcss/postcss) plugin to transform [W3C CSS color function][specs] to more compatible CSS.
+[PostCSS](https://github.com/postcss/postcss) plugin to transform CSS color function from editor draft of 'Color Module Level 4' specification to more compatible CSS.
+
+## Deprecated
+
+**⚠️ `color()` was changed to `color-mod()`. See [postcss-color-mod-function](https://github.com/jonathantneal/postcss-color-mod-function).**
+
+> There is a
+  [`color-mod`](https://github.com/jonathantneal/postcss-color-mod-function)
+  implementation.
+
+**⚠️ `color-mod()` has been removed from [Color Module Level 4 specification](https://www.w3.org/TR/css-color-4/#changes-from-20160705).**
 
 ## Installation
 
 ```console
-$ npm install postcss-color-function
+npm install postcss-color-function
 ```
 
 ## Usage
@@ -20,8 +30,10 @@ var colorFunction = require("postcss-color-function")
 var css = fs.readFileSync("input.css", "utf8")
 
 // process css
+// set preserveCustomProps to `false` by default `true`
+//for delete declarations with custom properties
 var output = postcss()
-  .use(colorFunction())
+  .use(colorFunction({preserveCustomProps: true}))
   .process(css)
   .css
 ```
@@ -75,8 +87,6 @@ Notes:
 - can be used on every value on any property,
 - some values can use add/subtract/scale modifiers or a direct value.
 
-[Read the specs][specs] for more information.
-
 ### Examples
 
 ```css
@@ -119,5 +129,3 @@ color(red shade(20%))
 ## [Changelog](CHANGELOG.md)
 
 ## [License](LICENSE)
-
-[specs]: http://dev.w3.org/csswg/css-color/#modifying-colors
diff --git a/index.js b/index.js
index c045b73..905dd88 100755
--- a/index.js
+++ b/index.js
@@ -6,10 +6,16 @@ var parser = require("postcss-value-parser")
 var colorFn = require("css-color-function")
 var helpers = require("postcss-message-helpers")
 
+var defaultOptions = {
+  preserveCustomProps: true,
+}
+
 /**
  * PostCSS plugin to transform color()
  */
-module.exports = postcss.plugin("postcss-color-function", function() {
+module.exports = postcss.plugin("postcss-color-function", function(options) {
+  options = Object.assign({}, defaultOptions, options)
+
   return function(style, result) {
     style.walkDecls(function transformDecl(decl) {
       if (!decl.value || decl.value.indexOf("color(") === -1) {
@@ -17,6 +23,10 @@ module.exports = postcss.plugin("postcss-color-function", function() {
       }
 
       if (decl.value.indexOf("var(") !== -1) {
+        if (!options.preserveCustomProps) {
+          decl.remove()
+          return
+        }
         result.messages.push({
           plugin: "postcss-color-function",
           type: "skipped-color-function-with-custom-property",
@@ -27,7 +37,7 @@ module.exports = postcss.plugin("postcss-color-function", function() {
             "`",
         })
         return
-      }
+      } 
 
       try {
         decl.value = helpers.try(function transformColorValue() {
diff --git a/package.json b/package.json
index 9025c91..b6c5fa9 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "postcss-color-function",
-  "version": "4.0.0",
+  "version": "4.1.0",
   "description": "PostCSS plugin to transform W3C CSS color function to more compatible CSS.",
   "keywords": [
     "css",
@@ -17,19 +17,20 @@
     "index.js"
   ],
   "dependencies": {
-    "css-color-function": "^1.3.0",
-    "postcss": "^6.0.1",
+    "css-color-function": "~1.3.3",
+    "postcss": "^6.0.23",
     "postcss-message-helpers": "^2.0.0",
-    "postcss-value-parser": "^3.3.0"
+    "postcss-value-parser": "^3.3.1"
   },
   "devDependencies": {
     "eslint": "^3.19.0",
+    "faucet": "0.0.1",
     "npmpub": "^3.1.0",
-    "tape": "^3.0.0"
+    "tape": "^4.10.1"
   },
   "scripts": {
     "lint": "eslint *.js index.js ./test/",
-    "test": "npm run lint && tape test",
+    "test": "npm run lint && tape test | faucet",
     "release": "npmpub"
   }
 }
diff --git a/test/fixtures/color.css b/test/fixtures/color.css
index 4ee21ac..335dc73 100644
--- a/test/fixtures/color.css
+++ b/test/fixtures/color.css
@@ -10,3 +10,9 @@ body {
 
   border-color: color(#999 a(0.8)) color(#999 a(0.8));
 }
+
+.withAlpha {
+  color: color(black a(80%) contrast(99%));
+  background-color: color(red a(50%) shade(50%));
+  border-color: color(red a(80%) tint(50%));
+}
diff --git a/test/fixtures/color.expected.css b/test/fixtures/color.expected.css
index 01cea60..f525b85 100644
--- a/test/fixtures/color.expected.css
+++ b/test/fixtures/color.expected.css
@@ -10,3 +10,9 @@ body {
 
   border-color: rgba(153, 153, 153, 0.8) rgba(153, 153, 153, 0.8);
 }
+
+.withAlpha {
+  color: rgba(255, 255, 255, 0.8);
+  background-color: rgba(128, 0, 0, 0.5);
+  border-color: rgba(255, 128, 128, 0.8);
+}
diff --git a/test/fixtures/delete-custom-properties.css b/test/fixtures/delete-custom-properties.css
new file mode 100644
index 0000000..1754afb
--- /dev/null
+++ b/test/fixtures/delete-custom-properties.css
@@ -0,0 +1,7 @@
+body {
+  color: color(var(--red));
+  color: color(var(--red) tint(50%));
+  background-color: color(red tint(50%));
+  color: color(var(--red) tint(var(--tintPercent)));
+  color: color(rgb(255, 0, 0) tint(var(--tintPercent)));
+}
diff --git a/test/fixtures/delete-custom-properties.expected.css b/test/fixtures/delete-custom-properties.expected.css
new file mode 100644
index 0000000..21d0172
--- /dev/null
+++ b/test/fixtures/delete-custom-properties.expected.css
@@ -0,0 +1,3 @@
+body {
+  background-color: rgb(255, 128, 128);
+}
diff --git a/test/index.js b/test/index.js
index d2c4801..e882c40 100755
--- a/test/index.js
+++ b/test/index.js
@@ -20,7 +20,7 @@ function compareFixtures(t, name, msg, opts, postcssOpts) {
   var actual = postcss().use(plugin(opts))
     .process(read(postcssOpts.from), postcssOpts).css
   var expected = read(filename("fixtures/" + name + ".expected"))
-  fs.writeFile(filename("fixtures/" + name + ".actual"), actual)
+  fs.writeFileSync(filename("fixtures/" + name + ".actual"), actual)
   t.equal(actual, expected, msg)
 }
 
@@ -106,3 +106,41 @@ test("logs message when color() contains var() custom property", function(t) {
     t.end()
   })
 })
+
+test(
+  "test delete custom properties with option preserveCustomProps `false`", 
+  function(t) {
+    postcss(plugin({preserveCustomProps : false})).process(
+      read(filename("fixtures/delete-custom-properties"))
+    ).then(function(result) {
+      var expectedDeclaration = [{
+        prop: "background-color",
+        value: "rgb(255, 128, 128)",
+      }]
+      // check left rules in body after clear
+      var declNodes = result.root.nodes[0].nodes
+      t.equal(
+        declNodes.length,
+        expectedDeclaration.length,
+        "expected " + expectedDeclaration.length +
+        " declaration length but got " + declNodes.length
+      )
+
+      t.equal(
+        declNodes[0].prop,
+        expectedDeclaration[0].prop,
+        "expected declaration with "+ expectedDeclaration[0].prop +
+        " property but got " + declNodes[0].prop
+      )
+
+      t.equal(
+        declNodes[0].value,
+        expectedDeclaration[0].value,
+        "expected declaration with "+ expectedDeclaration[0].value +
+        " value but got " + declNodes[0].value
+      )
+
+      t.end()
+    })
+  }
+)