Merge branch 'master' of https://github.com/d3/d3-interpolate

README.md

@@ -31,7 +31,9 @@ Note that the generic value interpolator detects not only nested objects and arr
 
 ## Installing
 
-If you use NPM, `npm install d3-interpolate`. Otherwise, download the [latest release](https://github.com/d3/d3-interpolate/releases/latest). You can also load directly from [d3js.org](https://d3js.org), either as a [standalone library](https://d3js.org/d3-interpolate.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-interpolate`. Otherwise, download the [latest release](https://github.com/d3/d3-interpolate/releases/latest). You can also load directly from [d3js.org](https://d3js.org), either as a [standalone library](https://d3js.org/d3-interpolate.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 using [color interpolation](#color-spaces), also load [d3-color](https://github.com/d3/d3-color).)
 
 ```html
 <script src="https://d3js.org/d3-color.v1.min.js"></script>