docs(material/radio): Update description for color input description on API page (#29333)

Author: amysorto

src/material/radio/radio.md

@@ -28,16 +28,6 @@ Individual radio-buttons inside of a radio-group will inherit the `name` of the
 `<mat-radio-group>` is compatible with `@angular/forms` and supports both `FormsModule`
 and `ReactiveFormsModule`.
 
-### Default Color Configuration
-The default color for radio buttons can be configured globally using the `MAT_RADIO_DEFAULT_OPTIONS` provider
-
-```
-providers: [{
-    provide: MAT_RADIO_DEFAULT_OPTIONS,
-    useValue: { color: 'accent' },
-}]
-```
-
 ### Accessibility
 
 `MatRadioButton` uses an internal `<input type="radio">` to provide an accessible experience.
@@ -56,7 +46,7 @@ should not use the `attr.` prefix when binding these properties, as demonstrated
 ```
 
 Prefer placing all radio buttons inside of a `<mat-radio-group>` rather than creating standalone
-radio buttons because groups are easier to use exclusively with a keyboard. 
+radio buttons because groups are easier to use exclusively with a keyboard.
 
 You should provide an accessible label for all `<mat-radio-group>` elements via `aria-label` or
-`aria-labelledby`. 
+`aria-labelledby`.

src/material/radio/radio.ts

@@ -74,6 +74,13 @@ export const MAT_RADIO_GROUP_CONTROL_VALUE_ACCESSOR: any = {
 export const MAT_RADIO_GROUP = new InjectionToken<MatRadioGroup>('MatRadioGroup');
 
 export interface MatRadioDefaultOptions {
+  /**
+   * Theme color of the radio button. This API is supported in M2 themes only, it
+   * has no effect in M3 themes.
+   *
+   * For information on applying color variants in M3, see
+   * https://material.angular.io/guide/theming#using-component-color-variants.
+   */
   color: ThemePalette;
 }
 
@@ -481,11 +488,17 @@ export class MatRadioButton implements OnInit, AfterViewInit, DoCheck, OnDestroy
     this._required = value;
   }
 
-  /** Theme color of the radio button. */
+  /**
+   * Theme color of the radio button. This API is supported in M2 themes only, it
+   * has no effect in M3 themes.
+   *
+   * For information on applying color variants in M3, see
+   * https://material.angular.io/guide/theming#using-component-color-variants.
+   */
   @Input()
   get color(): ThemePalette {
-    // As per Material design specifications the selection control radio should use the accent color
-    // palette by default. https://material.io/guidelines/components/selection-controls.html
+    // As per M2 design specifications the selection control radio should use the accent color
+    // palette by default. https://m2.material.io/components/radio-buttons#specs
     return (
       this._color ||
       (this.radioGroup && this.radioGroup.color) ||

tools/public_api_guard/material/radio.md

@@ -109,7 +109,6 @@ export class MatRadioChange {
 
 // @public (undocumented)
 export interface MatRadioDefaultOptions {
-    // (undocumented)
     color: ThemePalette;
 }