After installing Lazarus on Ubuntu, i got the same ugly IDE (colors,fonts,control design) as many mentioned here already.
Recompiling for gtk2 didn't fix anything in the first place, because the options don't match for that!
Here's the solution:
1. Click menu
Deutsch: "Werkzeuge/Lazarus erstellen einrichten ..."
English: "Tools/Rebuild Lazarus ..." (or similar, i'm not sure cuz using german)
2. Set all items in list to "Clean+Build" (rightmost icon), except the following:
CodeTools -> "None"
Package registration -> "None"
Samples -> "None"
3. Select "gtk2" in LCL interface
4. Check "clean all" | "Alles säubern" at top right corner
5. Check "with packages" | "Mit Packages" below lcl-groupbox
6. Check "restart.." | "Neustart ..." at bottom
7. Click "Create" | "Erstellen" button.
After that, lazarus should restart as a nice gnome/gtk2 application with correct fonts and colors and design of all controls.