If you're using Visual Studio classes/structures that have the correct namespace imported show up as light blue whereas ones that don't show up as normal text. An easy way to add the correct using statement (assuming the assembly containing the class is references - which System.Windows.Forms will be normally) you can put the cursor at the far right side of the name and a small red rectangle will show up. Put your mouse over this rectangle and a box will appear. Click the box and a menu shows up asking if you want to add the using statement.

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