diff --git a/README.md b/README.md
index f6d79b2..c29bed1 100644
--- a/README.md
+++ b/README.md
@@ -37,6 +37,8 @@ In addition to the ubiquitous and machine-friendly [RGB](#rgb) and [HSL](#hsl) c
 
 Cubehelix features monotonic lightness, while CIELAB and its polar form CIELCh<sub>ab</sub> are perceptually uniform.
 
+## Extensions
+
 For additional color spaces, see:
 
 * [d3-cam16](https://github.com/d3/d3-cam16)
@@ -45,12 +47,16 @@ For additional color spaces, see:
 * [d3-hcg](https://github.com/d3/d3-hcg)
 * [d3-hsluv](https://github.com/petulla/d3-hsluv)
 
+To measure color differences, see:
+
+* [d3-color-difference](https://github.com/Evercoder/d3-color-difference)
+
 ## Installing
 
-If you use NPM, `npm install d3-color`. Otherwise, download the [latest release](https://github.com/d3/d3-color/releases/latest). You can also load directly from [d3js.org](https://d3js.org), either as a [standalone library](https://d3js.org/d3-color.v1.min.js) or as part of [D3](https://github.com/d3/d3). AMD, CommonJS, and vanilla environments are supported. In vanilla, a `d3` global is exported:
+If you use NPM, `npm install d3-color`. Otherwise, download the [latest release](https://github.com/d3/d3-color/releases/latest). You can also load directly from [d3js.org](https://d3js.org), either as a [standalone library](https://d3js.org/d3-color.v2.min.js) or as part of [D3](https://github.com/d3/d3). AMD, CommonJS, and vanilla environments are supported. In vanilla, a `d3` global is exported:
 
 ```html
-<script src="https://d3js.org/d3-color.v1.min.js"></script>
+<script src="https://d3js.org/d3-color.v2.min.js"></script>
 <script>
 
 var steelblue = d3.rgb("steelblue");
diff --git a/package.json b/package.json
index 3889496..5717fc7 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,9 @@
 {
   "name": "d3-color",
-  "version": "1.4.1",
+  "version": "2.0.0-rc.1",
+  "publishConfig": {
+    "tag": "next"
+  },
   "description": "Color spaces! RGB, HSL, Cubehelix, Lab and HCL (Lch).",
   "keywords": [
     "d3",
diff --git a/src/cubehelix.js b/src/cubehelix.js
index bc31659..83536dd 100644
--- a/src/cubehelix.js
+++ b/src/cubehelix.js
@@ -1,6 +1,6 @@
 import define, {extend} from "./define.js";
 import {Color, rgbConvert, Rgb, darker, brighter} from "./color.js";
-import {deg2rad, rad2deg} from "./math.js";
+import {degrees, radians} from "./math.js";
 
 var A = -0.14861,
     B = +1.78277,
@@ -21,7 +21,7 @@ function cubehelixConvert(o) {
       bl = b - l,
       k = (E * (g - l) - C * bl) / D,
       s = Math.sqrt(k * k + bl * bl) / (E * l * (1 - l)), // NaN if l=0 or l=1
-      h = s ? Math.atan2(k, bl) * rad2deg - 120 : NaN;
+      h = s ? Math.atan2(k, bl) * degrees - 120 : NaN;
   return new Cubehelix(h < 0 ? h + 360 : h, s, l, o.opacity);
 }
 
@@ -46,7 +46,7 @@ define(Cubehelix, cubehelix, extend(Color, {
     return new Cubehelix(this.h, this.s, this.l * k, this.opacity);
   },
   rgb: function() {
-    var h = isNaN(this.h) ? 0 : (this.h + 120) * deg2rad,
+    var h = isNaN(this.h) ? 0 : (this.h + 120) * radians,
         l = +this.l,
         a = isNaN(this.s) ? 0 : this.s * l * (1 - l),
         cosh = Math.cos(h),
diff --git a/src/lab.js b/src/lab.js
index b27196e..645e1a5 100644
--- a/src/lab.js
+++ b/src/lab.js
@@ -1,9 +1,9 @@
 import define, {extend} from "./define.js";
 import {Color, rgbConvert, Rgb} from "./color.js";
-import {deg2rad, rad2deg} from "./math.js";
+import {degrees, radians} from "./math.js";
 
 // https://observablehq.com/@mbostock/lab-and-rgb
-var K = 18,
+const K = 18,
     Xn = 0.96422,
     Yn = 1,
     Zn = 0.82521,
@@ -85,7 +85,7 @@ function hclConvert(o) {
   if (o instanceof Hcl) return new Hcl(o.h, o.c, o.l, o.opacity);
   if (!(o instanceof Lab)) o = labConvert(o);
   if (o.a === 0 && o.b === 0) return new Hcl(NaN, 0 < o.l && o.l < 100 ? 0 : NaN, o.l, o.opacity);
-  var h = Math.atan2(o.b, o.a) * rad2deg;
+  var h = Math.atan2(o.b, o.a) * degrees;
   return new Hcl(h < 0 ? h + 360 : h, Math.sqrt(o.a * o.a + o.b * o.b), o.l, o.opacity);
 }
 
@@ -106,7 +106,7 @@ export function Hcl(h, c, l, opacity) {
 
 function hcl2lab(o) {
   if (isNaN(o.h)) return new Lab(o.l, 0, 0, o.opacity);
-  var h = o.h * deg2rad;
+  var h = o.h * radians;
   return new Lab(o.l, Math.cos(h) * o.c, Math.sin(h) * o.c, o.opacity);
 }
 
diff --git a/src/math.js b/src/math.js
index e94b840..66b172e 100644
--- a/src/math.js
+++ b/src/math.js
@@ -1,2 +1,2 @@
-export var deg2rad = Math.PI / 180;
-export var rad2deg = 180 / Math.PI;
+export const radians = Math.PI / 180;
+export const degrees = 180 / Math.PI;