Decided that I can not yet buy a background and need to make something simple and cute. And most importantly — quickly. My eight-year-old son helped me because he loves cutting and painting.
So, take all that you can find: any board and paints. A bristle brush and a piece of sponge.
First, saw and hammer the pieces together, it's important not to leave gaps.
Then take a water-emulsion or any other white paint. Sponge the entire surface.
Then make such random brush strokes with blue acrylic paint. Most importantly, along the fibres.
In a few minutes, when the paint gets dry, shade the strokes with the dry sponge you used for water-emulsion. The aim is to remove the contrast and leave brush dabs, not to smear.
This is the overall view.
Now add lemon yellow with a dry brush. Not across all the surface!
The main step. Take the thick bristle brush, a flit-brush, pick some water-emulsion paint, apply it so that blue and yellow dabs were seen. It's good if the traces of the brush are seen.
I think a background is good when it has a texture and colour, but does not kill an item in the photo. And most importantly, one can make any colour :)
Made a few examples with different objects.