Traditionally wedding cakes are white but that doesn’t mean your cake has to be white. Many couples are working with their bakers to create unique designs with colorful fondant or buttercream or colorful details on a white cake.
Have your mom go with you to the baker to see his portfolio and what non-white cakes look like. Your mom’s concern may be that a non-white cake would be too wacky for a wedding. A look at some traditional designs in a variety of colors may help her understand that color isn’t a weird option.
If you feel that you need to have a white wedding cake because it’s important to your mom, or because she’s paying the bills, you can always opt for a groom’s cake which is traditionally chocolate but generally accepted in any color, design and flavor.