def linear_combination(c1, c2, k1):
    """Returns medium color between c1 and c2"""
    k2 = 1.0 - k1
    r = int(k1 * c1[0] + k2 * c2[0])
    g = int(k1 * c1[1] + k2 * c2[1])
    b = int(k1 * c1[2] + k2 * c2[2])
    return r, g, b
