thank you for your contribution
as I see, you already adjusted the extension to follow the naming conventions... to make it 100% correct, please also change the package name of the extension and remove the underscore... rather than Simple_toast the correct name would be SimpleToast...
Also here in the App Inventor world we do not work with hex colors... we use color blocks
please change that in your logic, so the extension is compatible with the built-in color blocks, thank you
see also this discussion
https://community.appybuilder.com/t/preview-extension-palettecolor/471/8
Taifun
Trying to push the limits! Snippets, Tutorials and Extensions from Pura Vida Apps by 
Taifun.