I'm not sure what you mean by almost black... the text box is light green/light violet/light gray, I'd understand if it's hard to see it if the textbox was dark?
Unless if you mean that the default font is too small? Then there's an alternate dyslexic font option.
Do you mean the browser? Are you trying to play the browser version on Android? I don't think it's compatible. You would have to download the Android APK version.
