Yes, that's absolutely fine. As I said, the theme and limitation are open to interpretation. One colour of text on a different coloured background most definitely counts as being two colours!
As for the lack of visuals, I think as long as you don't use a really awful colour combination, you should be fine. I will definitely take it into account when calculating your overall score, and will not penalise you for your game being text based. I got started in game dev making text based puzzle games, so if you can make it work, I look forward to seeing your entry!
Best of luck!