Use backtick code blocks for syntax highlighting

55-01.md

@@ -91,11 +91,13 @@ blue resolution, using the structure shown in Listing 55.1.
 
 **LISTING 55.1 L55-1.C**
 
-     typedef struct -ModelColor {
-        unsigned char Red;   /* 255 = max red, 0 = no red */
-        unsigned char Green; /* 255 = max green, 0 = no green */
-        unsigned char Blue;  /* 255 = max blue, 0 = no blue */
-     } ModelColor;
+```c
+typedef struct -ModelColor {
+  unsigned char Red;   /* 255 = max red, 0 = no red */
+  unsigned char Green; /* 255 = max green, 0 = no green */
+  unsigned char Blue;  /* 255 = max blue, 0 = no blue */
+} ModelColor;
+```
 
 Here, each color is described by three color components—one each for
 red, green, and blue—and each primary color component is represented by