Flavourless Chocolate/Chocolate Alternative in Fudge
In white "chocolate" fudge the white chocolate adds fat, from cocoa butter, sugar and vanilla. White chocolate is mostly about texture and has little flavor of its own. In my opinion white chocolate isn't particularly useful in white fudge because the cocoa butter doesn't enhance the texture much and the sugar and vanilla are more easily (and inexpensively) added separately. In regular, chocolate, fudge there is no cocoa butter and the cocoa powder is used purely for the flavor.

Fudge is a creamy candy. It is creamy, and reminds us to some degree of chocolate, because of the small sugar crystals. The cocoa powder in chocolate fudge doesn't play a significant role in the texture of the candy.

You can leave the cocoa powder out of your chocolate fudge recipe and use other flavorings. 

As ChrisH wrote in a comment, it might be easier to simply start with a blank-slate fudge recipe that has no cocoa powder. It will likely be very similar.