I have a problem with text colour.
When you answer a question correctly, the bottom of the screen - the area that tells you if the answer is right or wrong - shows green text against a lighter green background. My problem is that if I have a typo, the green-on-green makes umlauts very difficult to see. I have to get my face up close to the computer screen to make it out. Likewise for incorrect answers, although red-on-red is not quite as bad.
Would it be possible to change (or have an option to change) the text colour? It's not a question of text size, but the lack of contrast between the two greens. Black text against a green (or red) background would be so much easier and would benefit people with less than perfect eyesight.