I’m red-green colorblind and find the colors of the Hard and Good feedback tick marks (orange and green) nearly impossible to distinguish. This means I’m often unsure whether I’ve hit the right button and have to back up and undo – I’d say this happens maybe 2-3 times per review session. I can tell them apart if I have them side by side, but when one flashes up for half a second with no additional context, it’s pretty much hopeless.
Here’s a simulator prepopulated with the two colors currently being used so you can get a decent idea of what I mean.
The ticks for Again and Easy are fine – blue stands no risk of being confused with anything on the red-green side of the spectrum, and the red is both much darker and has a different symbol. To distinguish Hard and Good, we could use different symbols (always a good practice anyway), or add a texture, or use significantly different shades (light green and dark orange or vice versa).
The colors must have changed at some point during a redesign, because I’ve only started to notice this being an issue within the last year or so and I’ve been using AnkiMobile for a decade.