as an example, the following patch vs default would somewhat enable this capability, although not perfectly:

--- a/scripts/plot/draw/private/__bar__.m       Mon Apr 29 16:25:41 2024 -0400
+++ b/scripts/plot/draw/private/__bar__.m       Mon Apr 29 17:08:35 2024 -0400
@@ -360,11 +360,15 @@
     addproperty ("facecolor", hg, "patchfacecolor", get (h, "facecolor"));
     addproperty ("linestyle", hg, "patchlinestyle", get (h, "linestyle"));
     addproperty ("linewidth", hg, "patchlinewidth", get (h, "linewidth"));
+    addproperty ("cdata", hg, "patchcdata", get (h, "cdata"));
+    addproperty ("facevertexcdata", hg, "patchfacevertexcdata", get (h, "facevertexcdata"));

     addlistener (hg, "edgecolor", @update_props);
     addlistener (hg, "facecolor", @update_props);
     addlistener (hg, "linestyle", @update_props);
     addlistener (hg, "linewidth", @update_props);
+    addlistener (hg, "cdata", @update_props);
+    addlistener (hg, "facevertexcdata", @update_props);

     if (isvector (x))
       addproperty ("xdata", hg, "data", x);
@@ -495,8 +499,8 @@

 function update_props (h, ~)
   kids = get (h, "children");
-  set (kids, {"edgecolor", "linewidth", "linestyle", "facecolor"},
-       get (h, {"edgecolor", "linewidth", "linestyle", "facecolor"}));
+  set (kids, {"edgecolor", "linewidth", "linestyle", "facecolor", "cdata", "facevertexcdata"},
+       get (h, {"edgecolor", "linewidth", "linestyle", "facecolor", "cdata", "facevertexcdata"}));
 endfunction

 function update_data (h, ~)

with that change, the following commands will change face colors in a couple different ways:

h = bar ([1, 2, 3, 4, 5]);
set (h, 'facevertexcdata', [0 0 0]);
set (h, 'facecolor', 'flat');
set (h, 'facevertexcdata', [0 0 0; 1 0 0; 0 1 0; 0 0 1; 1 1 1]);
set (h, 'facecolor', 'r');
set (h, 'facecolor', 'flat');

i'm not exactly sure why i need to cycle it from 'flat' to something else and back for it to recognize the facevertexcdata change. also i'm not sure why it's not looking at cdata, since the patch was defined with (x,y, 'cdata') in `__bar__`, but it shows the idea.