The bitmap is transparent, so the only thing that is not transparent is the text you wrote on it, which is convenient if you wanted to draw the image with text on another image.
If you set PictureBox2's background color to White, then the transparent bitmap with text would allow that white to show.
If you don't want the text to be drawn on a transparent bitmap, either draw a white filled rectangle in the bitmap after you create it, or use the Clear method and pass the color white to it, so it clears the bitmap to white.