Basically, you need to start up Modelsim:
1. Select on Menu: Tools > Edit Preferences. This will open up a "Preferences" dialog box.
2. In the dialog box, Select "Wave Windows" from "Window List" on the left-hand side. This will change the right-hand side of the dialog box to the "Wave Window Color Scheme" Listbox.
3. Select "waveBackground" from the ListBox. Select White color from the color palette.
4. Click Applied and your waveform background will change to white.
Should you change the background to white, the text will not be visible as they are white by default. Feel free to explore the other features in the ListBox for a better experience.
Hope it helps.