Yes and no. (Very helpful, right??)
Yes: You can change icon for "things" very easily in the app. However, you are limited to what icons SmartThings provides. Open up your device by hitting the 'gear' at top right, then select preferences.
Yes: You can change the background colors without too much effort, however this is more of a "hack" than a built in ability. It involves copying an existing device type into a custom device type, then editing two lines to change colors. It's a relatively easy process, but does take a bit of manual labor. And it has to be done for each new color combination you want.
No: You can not really change the layout of SmartThings (ie: 3 x whatever). You can group multiple things into a folder to organize it a little better.
Definitely check out this thread:
It's a bit involved, but doesn't look to be TOO hard. I haven't done anything with it myself but don't really look like much coding.