By default, asset nodes are translucent so you can partially see external nodes or connections underneath them. You can make asset nodes opaque by selecting Options > Opaque Assets from the Hypergraph or Hypershade options menu. See Opaque Assets.
You can also set the background for each asset in the Hypergraph to a custom image. This can help you quickly identify an asset by sight.
To customize the background of an asset in the Hypergraph