When I looked at the MLT XML of your project, I saw some "movit" properties on some producers, which means GPU processing. However, I see that the transition elements which are used for compositing/blending video tracks are using frei0r.cairoblend, which is what is used in CPU processing mode (GPU processing uses movit.overlay). If you open this project in CPU mode, then it works fine. If you open it in GPU processing mode, then it is using the wrong transition and shows this color difference when toggling the track composite button. This shows a couple of bugs: allowing it to be opened in GPU mode and some difference in RGB - YUV conversions. Moreover, this is reproduced in GPU mode only when Settings > Gamma is set to Rec. 709.