Why does the colour keep changing on this one?

I don’t understand what’s happening or why it’s happening and how to stop it. I uploaded a pic (yes it’s a sudoku grid don’t judge), made a new layer, picked a colour, but every time I go to write, the colour changes. I thought it was a bug in the app so I closed it, reopened it, still happens. If I go to another project, everything works perfectly. I don’t understand, please help I just wanted to play a game of sudoku with different colours for different numbers. I’ll join these two screen recordings so you can see my settings and the problem. Thank you for your help!:) Ps: I paid for the full version.