Do time color calculation with TZ aware time value.

src/widgets/datetime.rs

@@ -47,27 +47,28 @@ impl DateTimeWidget {
 
 impl Widget for DateTimeWidget {
     fn update(&mut self) -> Option<WidgetUpdate> {
-        let now = chrono::Local::now();
+        let (time, time_string) = match &self.tz {
+            Some(tz) => {
+                let tz: Tz = tz.parse().unwrap();
+                let now = chrono::Local::now();
+                let now = now.with_timezone(&tz);
+                (now.time(), now.format(&self.fmt).to_string())
+            }
+            None => {
+                let now = chrono::Local::now();
+                (now.time(), now.format(&self.fmt).to_string())
+            }
+        };
         let color = if let Some(colors) = &self.colors {
             colors
                 .iter()
-                .filter(|tc| tc.start < now.time())
+                .filter(|tc| tc.start < time)
                 .last()
                 .map(|tc| tc.color.clone())
         } else {
             None
         };
 
-        let time_string = match &self.tz {
-            Some(tz) => {
-                let tz: Tz = tz.parse().unwrap();
-                let now = now.with_timezone(&tz);
-                //TODO(wathiede): convert to timezone.
-                now.format(&self.fmt).to_string()
-            }
-            None => now.format(&self.fmt).to_string(),
-        };
-
         let mut data = Block::new().append_full_text(&time_string).clone();
         if let Some(color) = color {
             data.color(color);