Improve contrasts among buttons

[SnowballSH]

The design needs to have more contrast among buttons. For example, credible and not credible should be completely contrasting colors. Not all buttons should be green.

[SnowballSH]

In utils.dart, we proposed
const Color highlight = Color(0xFFF0EAD2);
const Color lightModeMedium = Color.fromARGB(255, 143, 162, 94);
const Color lightModeDark = Color.fromARGB(255, 79, 89, 52);
const Color darkModeMedium = Color(0xFFA98467);
const Color darkModeDark = Color(0xFF6C584C);

These colors, while green and brown look nice, the colors are a little too similar, and contrasts between buttons are insignificant.

Please plan and change the colors as well as gradients in the frontend code to make it look more vibrant and beautiful, preserving green and brown idea and the feel of the app. Don't make the colors too light or full though, since the background is a black and white map, so it should maintain a retro, environmental feel.