You have two options. First, you can use orange sweet potatoes, if you don't mind the color change. I do find orange sweet spuds have a little more water content (just a titch) than yellow, so maybe reduce the milk measure by 1 tbsp in both the cake and frosting. Another option is to use murasaki (japanase sweet potatoes). While hannah sweet potatoes have a yellow skin and underlying yellow flesh (see my video), murasaki spuds have purple skin with yellow flesh. The thing with murasaki spuds, however, is that some batches discolor when cooking. You can get grey streaks in the spuds. Also, I find these spuds have a little less moisture, so you may need 1-2 tbsp more milk for the batter and frosting. If possible, nab those hannahs!