*plug* Adventure Game Studio supports 8 and 16-bit color depths, while also supporting the 320x200, 320x240, 640x400,640x480, and 800x600 screen resolutions. Most, if not all of the stuff possible to do in it can be done by just clicking your mouse and naming certain things. Or, you can hard code the whole thing or certain areas to do what you want it to do. You can use it to make any type of game you want, from Sierra, to Lucas-Arts. You're not confined to create adventure games either, some of the more advanced users have created platform, action, RPG, and 2D/3D car driving games. *plug*
But, if you are looking to create genuine fan-Sierra games, you should use SCI Studio. SCI Studio is very versatile too. Once the new version of SCI Studio comes out, you can pretty much make whatever you want with it.