I will recommend doing this without macros because this method should be easy enough to implement.

Start by creating an inline circle and colouring it. Now select it and save it as a building block. I chose to put it in as an Autotext and assigned a category of 'Traffic Light'. Give it a name along the lines of the colour you chose. Now change the colour of the circle and save it as another Autotext/Traffic Light. Change it again and do the same so that you now have three Autotext/Traffic Light building blocks.
Next step is to add a Building Block Gallery Content Control to your form. You can change its properties so that it shows the members of the Autotext/Traffic Light.

The tricky part will be deciding WHERE to save the building blocks. If this only has to work on your machine, the default template of Normal or Building Blocks will be fine. However if you are intending this to work on other people's machines, the form should be saved as a template (dotx or dotm file) and you will need to save the building blocks into that template itself.

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Andrew Lockton
Chrysalis Design, Melbourne Australia