Rename d to delta.

src/main.rs

@@ -80,15 +80,15 @@ fn main() {
     for line in stdin.lock().lines() {
         seed += 1;
 
-        let mut d = 0;
+        let mut delta = 0;
 
         for c in line.unwrap().chars() {
-            d += match c {
+            delta += match c {
                 '\t' => 8,
                 _ => 1
             };
 
-            let (red, green, blue) = rainbow(freq, (seed + d) as f32 / spread);
+            let (red, green, blue) = rainbow(freq, (seed + delta) as f32 / spread);
 
             print!("{}", RGB(red, green, blue).paint(c.to_string()));
         }