Add tests for ansicolors function and new $Use...Colors variables.

src/types.h

@@ -238,6 +238,6 @@ typedef struct {
 /* Pure JSON */
 #define PSCAL_LEVEL3  3
 
-#define TERMINAL_BACKGROUND_UNKNOWN 0
-#define TERMINAL_BACKGROUND_DARK    1
-#define TERMINAL_BACKGROUND_LIGHT   2
+#define TERMINAL_BACKGROUND_UNKNOWN -1
+#define TERMINAL_BACKGROUND_DARK    0
+#define TERMINAL_BACKGROUND_LIGHT   1