If you choose to use a different colour for the border, now is the perfect time to fasten off the first colour, weave in the tails and attach the new colour in any of the corners. If you are not intending to work the square border, skip to Round 20. If you want to crochet the square border, continue with that pattern now.
Changing colour for Round 20:
Although you could add the new colour in any way you wish, the neatest way is by using a standing sc. If you choose this method, omit the ch1 and the first sc at the beginning of Round 20 and continue with the ch2 after the standing sc.
Round 20: Ch1, [(sc, ch2, sc) into the ch2 corner space, sc in 3rd loop or bpsc across {37 sts on each side in this round}] 4 times.
Ss into the top of the first st or cut yarn and finish with an invisible join. – 39 sts per side plus ch2 corner space
The inner part of your Guarding His Right square is now finished 🙂