Thank you ein, as much as that wasn't the exact point, but derived from it.
I did answer your question, Briggsy. A blue square symbolises water, a yellow for sand. Blue is symbolic of water. This type of symbolism has been used since before anybody alive on this earth was born. But regardless, how the game presents itself is irrelevant as to why it chooses this form. Did it choose it because it wanted to embellish days long gone and summon a sense of nostalgia, or because somebody else was already doing that, and doing it very well?