Coloring cube

# ok just slow
def main():
    n = int(input())
    pattern = "RGB"

    out = []
    app = out.append
    ix = 0
    for i in range(n):
        i3 = i % 3
        for j in range(n):
            ix = ((j % 3) + i3) % 3
            for _ in range(n):
                app(pattern[ix])
                ix = (ix + 1) % 3
            app("\n")
        app("\n")

    print("".join(out))


main()

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED