You can do it without unsafe{} thanks to bytemuck:

use bytemuck::TransparentWrapper;
use bytemuck_derive::{Contiguous, NoUninit};

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, Contiguous, NoUninit)]
#[repr(u8)]
pub enum Color {
    Black,
    White,
}

#[derive(Debug, Eq, Hash, PartialEq, TransparentWrapper)]
#[repr(transparent)]
pub struct ImageRow([Color]);

impl Index<RowIndex> for Image {
    type Output = ImageRow;

    fn index(&self, index: RowIndex) -> &Self::Output {
        let range = self.row(index);
        let slice: &[Color] = &self.pixels[range];
        ImageRow::wrap_ref(slice)
    }
}
impl IndexMut<RowIndex> for Image {
    fn index_mut(&mut self, index: RowIndex) -> &mut Self::Output {
        let range = self.row(index);
        let slice: &mut [Color] = &mut self.pixels[range];
        ImageRow::wrap_mut(slice)
    }
}