android:targetSdkVersion="20"，它应该< 21。

从manifest.xml中删除android:targetSdkVersion="21"它会起作用的! 从这一点上看，在你的apk中没有任何问题，这只是一个技巧，我应用这个，我在通知中发现了彩色图标

我认为现在谈论API 21已经太晚了，但我找到了一个简单的方法。

使用“自定义通知(自定义布局)”时，

RemoteView的

setImageViewResource(int viewId, int srcId);

and

setImageViewUri(int viewId, Uri uri); 

使这些图像白色的棒棒糖(API 21)。

但是当使用

setImageViewBitmap(int viewId, Bitmap bitmap);

图像不会变成白色面具!

我也遇到过同样的问题，那是因为我的应用通知图标不平坦。对于android版本，你的应用通知图标应该是扁平的，不要使用带有阴影的图标。

下面的代码在所有android版本上都运行得很好。

private void sendNotification(String msg) {

    NotificationManager mNotificationManager = (NotificationManager) this.getSystemService(Context.NOTIFICATION_SERVICE);

    Intent intent = new Intent(this, CheckOutActivity.class);

    PendingIntent contentIntent = PendingIntent.getActivity(this, 0, intent, 0);

    NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(
            this).setSmallIcon(R.drawable.ic_notification)
            .setContentTitle(getString(R.string.app_name))
            .setStyle(new NotificationCompat.BigTextStyle().bigText(msg))
            .setContentText(msg).setLights(Color.GREEN, 300, 300)
            .setVibrate(new long[] { 100, 250 })
            .setDefaults(Notification.DEFAULT_SOUND).setAutoCancel(true);

    mBuilder.setContentIntent(contentIntent);
    mNotificationManager.notify(new Random().nextInt(), mBuilder.build());
}

错误的图标

正确的图标

为了避免通知图标变成白色，使用“剪影”图标。透明背景图片。 你可以使用Irfanview来构建它们:

choose a picture, open in IrfanView, press F12 for the painting tools, clean picture if necessary (remove unwanted parts, smooth and polish) Image / Decrease Color Depth to 2 (for a black & white picture) Image / Negative (for a white on black picture) Image / Resize/Resample to 144 x 144 (use Size Method "Resize" not "Resample", otherwise picture is increased to 24 color bits per pixel (24 BPP) again File / Save as PNG, check Show option dialog, check Save Transparent Color, click Save, then click on the black color in the image to set the transparent color

Android似乎只使用drawablexxhdpi图片分辨率(144 x 144)，所以复制你的结果ic_notification.png文件到\AndroidStudio\Projects\ app\src\main\res\ drawablexxhdpi。在代码中使用. setsmallicon (R.drawable.ic_notification)，或者像Daniel Saidi上面建议的那样使用getNotificationIcon()。

你也可以使用Roman Nurik的Android Asset Studio。

Post android Lollipop release android has changed the guidelines for displaying notification icons in the Notification bar. The official documentation says "Update or remove assets that involve color. The system ignores all non-alpha channels in action icons and in the main notification icon. You should assume that these icons will be alpha-only. The system draws notification icons in white and action icons in dark gray.” Now what that means in lay man terms is "Convert all parts of the image that you don’t want to show to transparent pixels. All colors and non transparent pixels are displayed in white"

你可以通过这里的截图看到如何做到这一点的细节 https://blog.clevertap.com/fixing-notification-icon-for-android-lollipop-and-above/

希望这能有所帮助