add [r, g, b] field to triangle, so we can draw coloured objects (next: add ability to change current colour)

functional-core/app/app-init.sml

@@ -38,6 +38,9 @@ struct
       , openFilePath = ""
       , fileBrowser = Vector.fromList []
       , fileBrowserIdx = 0
+      , r = 0.0
+      , g = 0.0
+      , b = 0.0
       }
     end