For Paul.py

from copy import deepcopy
from typing import List


def propagate_color(matrix: List[List[str]], color: str) -> List[List[str]]:
    """Propagates color to all same colors that neighbor the color at [0,0]

    Note: only works for square matrices!
    """
    to_change: str = matrix[0][0]
    changed_matrix = deepcopy(matrix)
    for row in range(0, len(matrix)):
        for column in range(0, len(matrix)):
            if row == column == 0:
                changed_matrix[row][column] = color
            above = matrix[row - 1][column]
            left = matrix[row][column - 1]
            neighbors = above == to_change or left == to_change
            cell = matrix[row][column] == to_change
            if neighbors and cell:
                changed_matrix[row][column] = color

    return changed_matrix


def pretty_print(matrix: List[List[str]]) -> None:
    for row in matrix:
        print(row)


if __name__ == '__main__':
    print("Starting test...")
    matrix = [['R', 'B', 'R'],
              ['R', 'G', 'G'],
              ['R', 'R', 'B']]
    print("Starting Matrix")
    pretty_print(matrix)
    print("Changing to color 'B'")
    matrix = propagate_color(matrix, "B")
    pretty_print(matrix)
    print("Changing to color 'G'")
    matrix = propagate_color(matrix, "G")
    pretty_print(matrix)
    print("\nComplete.")