Soon you will be able to download additional tilesets and color schemes right from the app. For now, you can install them by copying to the DF Remote documents folder using iTunes File Sharing.
Additional tilesets for DF 0.47.05 will be available soon.
You can install any color scheme you find by renaming the file (usually colors.txt) to
colors-NAME.txt and copying it to the DF Remote documents folder.
Most of the tilesets include creature graphics. If you want to add more graphics sets, put their files (usually, a text file and a folder with images, or several of them) in a folder named
graphics-NAME and copy it to the DF Remote documents folder.