Darken file size suffixes

I think this is necessary because 'bytes' currently has no 'B' suffix, and it's
kind of hard to distinguish a long number from a suffix.

file.rs

@@ -89,13 +89,13 @@ impl<'a> File<'a> {
         if self.stat.kind == io::TypeDirectory {
             Black.bold().paint("-")
         } else {
-            let size_str = if use_iec_prefixes {
+            let (size, suffix) = if use_iec_prefixes {
                 format_IEC_bytes(self.stat.size)
             } else {
                 format_metric_bytes(self.stat.size)
             };
 
-            return Green.bold().paint(size_str.as_slice());
+            return format!("{}{}", Green.bold().paint(size.as_slice()), Green.paint(suffix.as_slice()));
         }
     }
 

format.rs

@@ -6,19 +6,19 @@ static IEC_PREFIXES: &'static [&'static str] = &[
     "", "Ki", "Mi", "Gi", "Ti", "Pi", "Ei", "Zi", "Yi"
 ];
 
-fn format_bytes(mut amount: u64, kilo: u64, prefixes: &[&str]) -> String {
+fn format_bytes(mut amount: u64, kilo: u64, prefixes: &[&str]) -> (String, String) {
     let mut prefix = 0;
     while amount > kilo {
         amount /= kilo;
         prefix += 1;
     }
-    format!("{}{}", amount, prefixes[prefix])
+    return (format!("{}", amount), prefixes[prefix].to_string());
 }
 
-pub fn format_IEC_bytes(amount: u64) -> String {
+pub fn format_IEC_bytes(amount: u64) -> (String, String) {
     format_bytes(amount, 1024, IEC_PREFIXES)
 }
 
-pub fn format_metric_bytes(amount: u64) -> String {
+pub fn format_metric_bytes(amount: u64) -> (String, String) {
     format_bytes(amount, 1000, METRIC_PREFIXES)
 }