Changing material color from dictionary (C#)

I've been working on an application in which the user loads a 3D model representing a part (important for context as I delve into the situation) into the environment and has the ability to adjust the transparency of that model. I have a working solution for this currently:

 Material partMat =
     app.currentPart.GetComponent<MeshRenderer>().material;
 Color partColor = partMat.color;
 partColor.a = val;
 partMat.color = partColor;

This solution loads the GameObject containing the model ( app.currentPart) and successfully changes its alpha channel to val, the parameter of the slider callback method from which this code was taken.

However, I have also recently implemented a change to my application such that the part can be broken up into its features, each represented by a GameObject containing a 3D model of its own (each such object is a sibling of one another under an empty GameObject). The only real difference in structure is that rather than referring to a sole GameObject app.currentPart, I refer to app.currentFeatures, which is a Dictionary<string, GameObject>. I want to adjust the transparency the same way. Some Googling led me to approach it this way:

 List<string> keys = new List<string>(app.currentFeatures.Keys);
 foreach (string featName in keys)
 {
     Material featMat =
         app.currentFeatures[featName].GetComponent<MeshRenderer>().material;
     Color featColor = featMat.color;
     featColor.a = val;
     featMat.color = featColor;
     app.currentFeatures[featName].GetComponent<MeshRenderer>().material = featMat;
  }

However, this yields no changes to the transparency of these models at runtime. I know that app.currentFeatures is correctly populated because if I print featName each iteration, it is correct. My suspicion is that this code is editing a copy of the GameObject rather than the one loaded into the environment, but I feel like I've tried pretty much all the different angles for getting the object itself.

Since submitting this question for moderation, I tried another approach based on the object hierarchy rather than my script variables/containers:

 foreach (MeshRenderer featMesh in app.partContainer.GetComponentsInChildren<MeshRenderer>())
 {
    Material featMat = featMesh.material;
    Color featColor = featMat.color;
    featColor.a = val;
    featMat.color = featColor;
 }

My thought was that referring directly to the children of app.partContainer (the empty GameObject holding the part/features as children) would solve this problem, but unfortunately, it did not.

UPDATE: I have since changed the specifications of my application significantly such that each feature has a type and each type corresponds to a uniquely colored material. When I implemented this, suddenly the problem went away entirely. I still would like to see this original question answered just in case others run into the same issue, though.