contentBackgroundColor/Alpha attributes aren't displaying in MXML

Steps to reproduce:
1. Create an mxml tag for either <s:TextInput or <s:TextArea
2. Start typing one of the attributes "contentBackgroundColor" or "contentBackgroundAlpha"
3. The attributes do not display in FB's list of available attributes. Type them in anyway, i.e. contentBackgroundColor="0xFF0000"
4. Compile and run. The compiler throws no errors. The application runs. However, the components' appearance is unchanged.