fix warning color in teachertool

Author: jwunderl

theme/color-themes/arcade-orange.json

@@ -76,6 +76,11 @@
         "pxt-link-hover": "#204467",
         "pxt-focus-border": "#0078D4",
 
+        "pxt-warning": "#FFD43A",
+        "pxt-warning-foreground": "#000000",
+        "pxt-warning-hover": "#FFCE21",
+        "pxt-warning-alpha10": "#FFD43A19",
+
         "pxt-colors-purple-background": "#6B4F76",
         "pxt-colors-purple-foreground": "#FFFFFF",
         "pxt-colors-purple-hover": "#4f3b57",