This A4 layout has a vintage (not sure my mam will want to know I've described her photo as vintage!) photograph but a modern feel. I never work in A4 but decided to try it and see what I thought. I have concluded that I find this size a bit restricting if you want to use more than one photograph (6" x 4") but it is great if you want to frame your layout as A4 frames are easier to find than 12 x 12 or if you have smaller photographs.
I used modern colours mixed with muted as well as printed acetate and it worked well for me, however I won't be in a hurry to swap from 12 x 12 to A4 but it was an interesting experiment.