Fill options for objects have changed entirely between 11 and 12. FM Inc warned us in advance that the fill effects would disappear after 11, but it still caught a lot of people by suprise.
Items which have pre-12 fills will retain those effects during converted, but that option is not be available among the tools in 12, so, if you change it, you can't go back later.
You can copy an old item which has a fill effect and repoint that field object to another field, which may allow retaining the pre-12 format, but you cannot create a new item and apply the old effects.
We now have the option for fill with colors, gradients, or images created outside of FileMaker, actually giving us a wider range of options, but, alas, not all of the old options.
This was part of the change when moving to a CSS-based layout generated layout design in 12.