Strange simple question about text

I am new to AI. I am editing a logo created for me. I expect the closed portions of closed letters (A, B, D etc) to be in my background color. But once I change the color of the letters (say from black to blue), the enclosed sections fill with that color as well. Try as I might I cannot find a way to either make them transparent so as to see the background, or fill them with my preferred background. The fill in with the letters, so that an O for example becomes a filled ellipse.

This comes from my not knowing something fundamental about text, I suppose. Please think of a hint with which I might change the fill of the letters as I please, and still look through the O, the P, the Q etc to see the background color.

Thank you.