Message Parts that are larger than 2k need to be manually downloaded and shown. The bubble is showing a a gray area because the image hasn't been downloaded.
For more information about Rich Content, check out this guide:
TIP:You can tell layerClient to automatically download specific mimetypes or content over a specific size. To do this you can set the `autodownloadMIMETypes` or `autodownloadMaximumContentSize` properties on `LayerClient`.
// Download all JPEG's, PNG's, GIF's automatically self.layerClient.autodownloadMIMETypes = [NSSet setWithObjects:@"image/jpeg", @"image/png",@"image/gif",nil];
// Download content that's up to 100 KB automatically self.layerClient.autodownloadMaximumContentSize = 1024 * 100;