Hackers Help: Turning Erikslund into picture frame?

Photo: IKEA.com

Hi all

I bought an Erikslund picture recently, which has exactly the right dimensions to frame a painting I already have.

I have undone the staples to remove the back, and removed the glue keeping the glass in place, and replaced it with a custom-cut pane of clear PVA.

The problem I have is that the inside of the frame, which was hidden due to the frosted glass, now shows through since I am mounting my painting at the back of the frame (deep-mounted) – and it is untreated, while the rest of the frame which was always visible, is black.

So what paint should I use to make the frame more uniform? Any old black wood paint from my local hardware? Spray paint?

Any ideas please?