How do I do that using the web browse?
Sorry, I assumed wrong, there does not seem to be a way to add anything to the library from the Web browser.
So how can I SHARE images as a reference files to the HEX colours?
Not quite neat, but this may work for you as a workaround
1. On the Adobe Capture CC iOS app (COLORS) tap on the theme to open preview
2. On Preview tap the share icon
3. You should see "Export as..." on the share menu
4. Choose Image
5. Choose Mail and email the same to your collaborators.