Well one thing I found out is that the fonts can't be changed in FireMonkey! You can set it to a different font but when you run it on a device it will go to the default one.
If you want to change the background color for the memo you should add a stylebook to your form and load a style file you want(Like the default light iOS style). When you have loaded a style go to memostyle and change de background.
Hope this helps!