Each sky condition is assigned a set of colors for the header UI and app background. The color system is based off a gradation between severity of sky conditions.
The illustrations assets are layered so they can transition onto the screen with some parallax. The layered system also allows us to reuse some common assets (like cloudy backgrounds), saving on filesizes and resources.
There are two versions of each icon. One for use on white or very light backgrounds, another for use on color or dark backgrounds