Naive micro-optimization of your program (namely, things like FF is 1 char shorter than [F]) got that down to 40 chars:

    [[[[[[[[[[[[[[[FF]]]]]]]RRF[RRR]]]]]]]]]

I then found a solution in 37 which uses a slightly different approach (namely, create a pattern that spans the full X and Y output space, then shift it by one step each iteration):

    [[[[[[[[[[[[[[[[FFF]]]]]R]]]F]]]]]]]]