This is highly, highly conceptual, because I lack the tools and skills for art, BUT this is broadly how I envision the pattern:

The largest and darkest crescents form permanents lines that might reflect the edges of major lobes of the cloud. These are widely spaced, and The overall pattern fades from dark to light as it travels inward to the next permanent line. Smaller puffs on the face by smaller crescents. I've found I like the look best when they're inside the major crescent rather than outside.
Interior features are similar, but they are isolated and formed from lighter shades. My idea is that as she ages, smaller and smaller details of the cloud are formed by smaller crescents.

The top row of sample colors is the range from darkest shadow to brightest highlight on her back, the lower samples are the same for her belly. Her actual pattern would fade smoothly from shadow to highlight.