Coldix

I have just purchased Affinity Photo. Some of the cameras I use are Sigma Merrill Dp cameras with the Foveon sensors. When I open a RAW file from one of these cameras I am getting strange and uneven colour casts. Greenish in some parts and magenta in others. I shoot simultaneous RAW and jpegs with these cameras and the jpeg file opens with natural colours. Can anyone suggest what is happening with the RAW files? Thank you.