With OLED displays such as yours (SAMOLED), there is no "backlight", meaning all light produced comes from the actual pixels. In order for a pixel to produce light, it uses power, and the brighter the image, the more power required. So to answer your question, yes, you are correct.
Using a darker wallpaper, using a dark icon theme, anything you can do to reduce or eliminate white backgrounds, and turning down total screen brightness will all go a long way toward reducing battery consumption. There is even a dark Googe search that can be used in place of the default Google search, with black backgrounds and white text which consumes less power.