[improvement] Radio: add checked-color prop (#2129)

packages/radio/en-US.md

@@ -11,6 +11,7 @@ Vue.use(Radio);
 ### Usage
 
 #### Basic Usage
+
 Use `v-model` to bind the name of checked radio
 
 ```html
@@ -39,6 +40,12 @@ export default {
 </van-radio-group>
 ```
 
+#### Custom Color
+
+```html
+<van-radio checked-color="#4b0">Radio</van-radio>
+```
+
 #### Inside a Cell
 
 ```html
@@ -62,6 +69,7 @@ export default {
 | disabled | Whether to disable radio | `Boolean` | `false` |
 | label-disabled | Whether to disable label click | `Boolean` | `false` |
 | label-position | Can be set to `left` | `String` | `right` |
+| checked-color | Checked color | `String` | `#1989fa` | - |
 
 ### RadioGroup API