I can select them, move them, resize them. How do I create them or change the color?
Only by patching and modifying the Aperture application bundle or creating a copy of the theme from inside the bundle and installing it in your user library. The frames are png-files built into the program (Cream_lined_frame_sm_L.png, /Cream_lined_frame_sm_P.png), controlled by property list files and reside in the folder
/Applications/Aperture.app/Contents/Resources/Book Themes/Photo Journal/Extra Large/Frames/
To change the color of the frames you would have to create a copy of the "/Applications/Aperture.app/Contents/Resources/Book Themes/Photo Journal" theme and install it in your User Library (your home folder/Library/Application Support/Aperture/Book Themes/) under a new name, then edit the png-files to your liking and use your custom theme.