For Material UI 7 you add the colors under colorSchemes in the theme https://mui.com/material-ui/customization/palette/#color-schemes

const theme = createTheme({
  colorSchemes: {
    light: {
      palette: {
        primary: {
          main: '#FF5733',
        },
      },
    },
    dark: {
      palette: {
        primary: {
          main: '#E0C2FF',
        },
      },
    },
  },
});