Fix some blank panels not having matching background color

src/Makefile

@@ -169,6 +169,11 @@ $(BUILD_DIR)/%.c.o: %.c
 	@echo "Compiling $<"
 	$(SILENT)$(CC) $< $(BUILD_C_FLAGS) -c -o $@
 
+$(BUILD_DIR)/Rack/src/core/Blank.cpp.o: Rack/src/core/Blank.cpp
+	-@mkdir -p "$(shell dirname $(BUILD_DIR)/$<)"
+	@echo "Compiling $<"
+	$(SILENT)$(CXX) $< $(BUILD_CXX_FLAGS) -UPRIVATE -D'nvgRGB(r,g,b)=nvgRGBblank(r,g,b)' -c -o $@
+
 $(BUILD_DIR)/Rack/src/core/%.cpp.o: Rack/src/core/%.cpp
 	-@mkdir -p "$(shell dirname $(BUILD_DIR)/$<)"
 	@echo "Compiling $<"

src/override/dep.cpp

@@ -20,6 +20,8 @@
 #include <cstdio>
 #include <cstring>
 
+#include "nanovg.h"
+
 // fix blendish build, missing symbol in debug mode
 #ifndef NDEBUG
 extern "C" {
@@ -39,6 +41,14 @@ float FollowerBase::efGainMaxDecibelsDebug = 12.0f;
 }
 #endif
 
+// Special nvgRGB for blank panels
+extern "C" {
+NVGcolor nvgRGBblank(unsigned char, unsigned char, unsigned char)
+{
+    return nvgRGB(0x20, 0x20, 0x20);
+}
+}
+
 // Compile those nice implementation-in-header little libraries
 #define NANOSVG_IMPLEMENTATION
 #define NANOSVG_ALL_COLOR_KEYWORDS