How to simply change the background colour of a cell inside a TableView

[VRonin]

If you call addMaskedRole passing either Qt::DisplayRole or Qt::EditRole any change will stay in the proxy and not be passed to the source model.

You should only mask the roles that you need, in this case Qt::BackgroundRole.

If it's still not clear, please post us the code using RoleMaskProxyModel and we'll be more specific on the changes to make