fixup! fix(material/core): fix opacity in elevation mixin

Author: skrtheboss

src/material/core/style/_elevation.scss

@@ -48,16 +48,16 @@ $prefix: 'mat-elevation-z';
     $ambient-z-value: map.get(mdc-elevation.$ambient-map, $zValue);
 
     $color-opacity: if($opacity != null, $opacity, 1);
-    $umbra-color: rgba($color, mdc-elevation.$umbra-opacity * $color-opacity);
-    $penumbra-color: rgba($color, mdc-elevation.$penumbra-opacity * $color-opacity);
-    $ambient-color: rgba($color, mdc-elevation.$ambient-opacity * $color-opacity);
+    $umbra-color: compute-color-opacity($color, mdc-elevation.$umbra-opacity * $color-opacity);
+    $penumbra-color:
+      compute-color-opacity($color, mdc-elevation.$penumbra-opacity * $color-opacity);
+    $ambient-color: compute-color-opacity($color, mdc-elevation.$ambient-opacity * $color-opacity);
 
     $box-shadow: (
       #{'#{$umbra-z-value} #{$umbra-color}'},
       #{'#{$penumbra-z-value} #{$penumbra-color}'},
       #{$ambient-z-value} $ambient-color
     );
-
     @include mdc-elevation.shadow($box-shadow);
   }
 }
@@ -94,3 +94,12 @@ $prefix: 'mat-elevation-z';
     $easing: $transition-timing-function) {
   transition: private-transition-property-value($duration, $easing);
 }
+
+@function compute-color-opacity($color, $opacity) {
+  @if meta.type-of($color) == color and $opacity != null {
+    @return rgba($color, $opacity);
+  }
+  @else {
+    @return $color;
+  }
+}