There's a dropdown for this, but if you're constantly switching between a wide range of custom colors it's way too time-consuming. It's not too bad as I have used up the 1-9 keys for my colors, but that only work with 1 tool. Imagine if we could assign keys 1-9 for colors only, keeping the separate keyboard shortcuts for changing tools: the number of tools quickly accessible literally multiples! I will try and hack the source code in the future when I have time to make it work this way as a start, but I'm not that good: I'll come back to this post if I discover / program anything useful that could speed up development times on this. :)
For now, here's a workaround in case you run out of the 9 slots that come with a shortcut, which still allows you to work fairly quickly: - from the top menu: 'Settings' > 'Toolbars Shown' > 'Quick Annotation Toolbar' (there seemed to be a bug which cause the "standard" 'Annotation Toolbar' to appear when the 'Quick Annotation Toolbar' was activated, so I just removed all items from all annotation toolbars by going into 'Settings' > 'Configure Toolbars...' - kind of counter-intuitive, but it worked I guess) - you can move the toolbar to different areas of the screen by dragging the parallel bars (I have my cursor on them in the screenshot That was good enough for me, but there's a discussion space here for a reason, I'm curious to know if anyone else has any issues 👀. Keyboard shortcuts still remain the best for screen real estate and speed
I'd also like to point out I have tried other PDF readers before settling with Okular, which explains why I am willing to build on Okular's solid functionality rather than try to bring other PDF readers with more features to be as stable as Okular. I figured out a way to add keyboard shortcuts for colors to [pdf-tools for Emacs](https://github.com/vedang/pdf-tools/discussions/332), but sadly the wealth of customisation options available in `Elisp` were pointless when the reader would crash with 100-page documents: in Okular I have heavily annotated image-dense PDFs whilst scrolling quickly through them and the experience has always been breathtakingly smooth on a computer as (relatively) low-power as the Raspberry Pi 5, greatly surpassing Zotero for example (which I was also able to crash in that scenario), from which I was able to transition despite its useful features, as there are ways to do the same things and better with Okular plus [searching inside PDF annotations via CLI](https://gist.github.com/SuperCowProducts/af05f34f03197bfefc80712d96d54a1e). I still took a very long time to start using Okular on a daily basis due to it's Windows/Linux-only availability, although I'm excited to test it on a mobile OS like Ubuntu Touch and make some adjustments if necessary, so that it's usable (mainly resizing controls and making sure everything's touch friendly, although knowing KDE is moving in that direction I should hopefully have a headstart in that area). Once that is done, Okular should be ready to use on any device, so long as it's running Linux.
Screenshot link: https://postimg.cc/bsnxXrwf Doesn't show the cursor actually, but parallel lines should be visible, just reply otherwise 👍