A dark blue to make the FF squares stand out more?
Oh dear, I've just realised I'm reading about quilterisering, NO, I won't be doing any myself! Whilst I admire the ones other people make, there is no room in my house for them - I actually like plainer colours. All those different colours would really mess with my OCD, I'd have had to just use blues for the CF squares, and they'd have to symmetrical! And possibly a dark red for the border then, although that's probably one colour too many for me!
Anyway, ignore me, this is a great tutorial from a great quilterist