edit error messages and add try block to draw-image.

SmoulderingBeachBall/InternalServices.fs

@@ -9,7 +9,7 @@
         let validateDimension dimension =
             match dimension with
             | dimension when dimension <= 0 -> 
-                invalidArg "dimension" "The width and height must be greater than 0."
+                invalidArg "dimension" "[ERROR] The width and height must be greater than 0."
             | _ -> ()
 
         let validateDirectory filePath =

SmoulderingBeachBallCLI/ConsoleCommands.fs

@@ -3,11 +3,8 @@
     module ConsoleCommands =
 
         open System
-        open Console.Waterworks
-        open SmoulderingBeachBall.Domain
         open SmoulderingBeachBall.Services
         open Validation
-        open System.Drawing
 
         let showEndOfCommandMessage = "[INFO.] Execution completed."
 
@@ -16,10 +13,14 @@
         let exit () = Environment.Exit (Environment.ExitCode)
 
         let ``draw-image`` imgWidth imgHeight mainColour path =
-            buildBasicSpec imgWidth imgHeight mainColour path
-            |> makeImage
-            |> Async.RunSynchronously
-            showEndOfCommandMessage
+            try
+                buildBasicSpec imgWidth imgHeight mainColour path
+                |> makeImage
+                |> Async.RunSynchronously
+                showEndOfCommandMessage
+            with
+            | :? ArgumentException as ex -> ex.Message
+            | _ as ex -> ex.Message
 
         let ``draw-borderedImage`` () =
 

SmoulderingBeachBallCLI/Validation.fs

@@ -26,8 +26,9 @@
             colourList 
             |> Map.find (colour.ToLower())
         | false ->
-            invalidArg "Colour" "[ERROR] The colour specifed is invalid."
-            // "Please use the ListAvailableColours command for a list"?
+            invalidArg "Colour"
+                (String.Concat("[ERROR] The colour specifed is invalid.\n",
+                    "Please use the 'list-colours' command to see what you can use."))
 
     let parsePath (path: string) =
         match path with