Hello,
You could use the Masking capabilities available in Amplify Color. For your specific requirements you would have to make some custom changes, we recomend checking out the Fog of War sample below as a starting point.
Unity 4/5 Fog of War Example:
Blog Post -
Sample DownloadWe also provide a dynamic mask example for AC, be sure to check it out.
DownloadLet us know if you run into any Amplify Color issues, we would be happy to help.
Thanks!