I have wanted to do something to decorate them, but was unsure what until I saw these two pins on Pinterest:
Bibus vintage rouge (etsy.com)
I loved the idea of adding a pop of colour, but just on the inside. So I went to the paint shop and bought some Bright Orange, almost a Tiffany blue, and a turquise green.
I painted six shelves in various shades - three of each. For the orange I painted one first, then topped up the test pot with white to do the other (each crate used just over half a pot) and then for the third I topped it back up with white to get the lightest shade.
I stacked them up (Nathan will bolt them together sometime, and add a top) and then hung some DIY art and a photo above. I think he's pretty happy!