Basic law of multiply and white: white disappears. Perhaps experiment with a different blend mode and a grayscale instead of white?
that's because the text is white. you can't 'multiply' by nothing, so to speak.
To get the text to become a tint of the background colour I would use the Swatch Panel and apply the colour to the text then in the Tint value option change it to the desired tint value you are happy with.
The multiply option in blending mode will blend the top colour (your text colour) with the background colour it is on and as your text colour is whitish it will disappear once you blend it with the darker background colour.