11 or so Android Ebook Reader Apps for Academic Writing Workflows: Annotations are Hard
Here’s my personal comparison of Android ebook readers for my Boox eink tablet. I would love to add drawings as annotations. Ratta Supernote devices do this splendidly by storing the pencil input directly, without handwriting recognition. (Example here.) This is the gold standard. Everything else requires multiple apps (to draw a diagram, for example) and import/export (of notes or EPUB book locations), which is also acceptable, but not ideal.
BOOX Vector PDFs Are Already Colored

After my interesting journey into replacing greyscale values in the vector PDF export of Onyc BOOX Notes, some brainiac on Mastodon pointed out that there are non-grey colors I could use. (Seriously, thank you Jeroen :))
Colorize Onyx BOOX Notes Vector PDFs (Really Rough Edition)

Sacha Chua has this nice Python script to colorize her SuperNotes sketches. Can’t be that hard to apply color replacement to the notes from BOOX devices, can it?!?! I had this exported vector PDF lying around:
Boox NeoReader Annotation Export Is Meh
When you use the built-in “NeoReader” on a Boox tablet, you get the best pencil input and quite good highlighting and annotation support. If you don’t have a Onyx Boox eink tablet with that app installed, don’t bother looking for it on the Android/Google Play Store – that app is not available anywhere else, it seems. And the app of the same name on the Play Store is a QR Code Reader.