diff --git a/config.cpp b/config.cpp
index 77e59f1a..a942d42a 100644
--- a/config.cpp
+++ b/config.cpp
@@ -3295,6 +3295,7 @@ EX int config3 = addHook(hooks_configfile, 100, [] {
     });
 
   param_ccolor(ccolor::which, "pattern");
+  param_str(ccolor::color_formula, "color_formula");
   });
 
 EX void switchcolor(unsigned int& c, unsigned int* cs) {
diff --git a/pattern2.cpp b/pattern2.cpp
index c25eed6d..eba9ac70 100644
--- a/pattern2.cpp
+++ b/pattern2.cpp
@@ -1672,7 +1672,10 @@ EX namespace ccolor {
   EX string color_formula = "rgb(to01(x),to01(y),to01(z))";
 
   EX data formula = data("formula", always_available, CCO {
-    return patterns::compute_map_function(c, color_formula);
+    color_t col = patterns::compute_map_function(c, color_formula);
+    bool wall = (col & 0xFF);
+    col >>= 8; if(wall) col |= 0x1000000;
+    return col;
     }, {});
 
   EX data threecolor = data("threecolor", [] { return geosupport_threecolor(); }, CCO {