pcrlock: exclude red and green color ranges

Using red and green in the output is rather confusing as that is
normally associated with good or bad like in the checkmark columns.
So let's exclude those colors from the display.

Co-authored-by: Akarithos <277667353+Akarithos@users.noreply.github.com>

src/pcrlock/pcrlock.c

@@ -2098,6 +2098,18 @@ static const char *ansi_true_color(uint8_t r, uint8_t g, uint8_t b, char ret[sta
         return ret;
 }
 
+/* red and green colors usually have good/bad meaning. So exclude color ranges that look too red- or
+ * greenish. See https://en.wikipedia.org/wiki/Hue */
+static double map_pcr_to_hue(uint32_t pcr) {
+        double exclude_red_range = 60.0;
+        double exclude_green_range = 60.0;
+        double h = (360.0 - exclude_red_range - exclude_green_range) / (TPM2_PCRS_MAX - 1) * pcr;
+        h += exclude_red_range / 2;
+        if (h > 120 - exclude_green_range / 2)
+                h += exclude_green_range;
+        return MIN(h, 360 - exclude_red_range / 2);
+}
+
 static char *color_for_pcr(EventLog *el, uint32_t pcr) {
         char color[ANSI_TRUE_COLOR_MAX];
         uint8_t r, g, b;
@@ -2108,7 +2120,7 @@ static char *color_for_pcr(EventLog *el, uint32_t pcr) {
         if (el->registers[pcr].color)
                 return el->registers[pcr].color;
 
-        hsv_to_rgb(360.0 / (TPM2_PCRS_MAX - 1) * pcr, 100, 90, &r, &g, &b);
+        hsv_to_rgb(map_pcr_to_hue(pcr), 100, 90, &r, &g, &b);
         ansi_true_color(r, g, b, color);
 
         el->registers[pcr].color = strdup(color);