The primary difference between Decora Lolita (or Decololi) and OTT Sweet Lolita is that, most of the time OTT Sweet Lolita tends to be more thematic and color coordinated. But the terms are often interchangable.
Decora Clothing == Popular colors in Decora clothing are black, dark pink, and light pink. Neons are acceptable. Plain shirts with hoodies can be paired with skirts with a tutu look. Stockings, leg warmers, arm warmers, and knee socks are layered on top of each other. Popular accessories include anything in leopard print and/or dental masks with patterns.