Since Materia is similar to MD2, I believe more colors should be added to it. In the GTK theme, the only colors present are greys and whites. In the Flutter MD2 Preview, (link here --> https://flutter.github.io/samples/web/material_3_demo/#/) if you switch to the MD2 theme in the top right corner, there is a different color other than purple. This is present with different colors in other MD2 apps.