Materials
cardboard box
white piece of fabric (a sheet or cotton muslin works well for this)
a piece of white construction paper (large enough to fit in the box)
a fluorescent desk lamp
Cut the sides and top from your box - leave 'frames' of cardboard so that you can have something to drape the fabric over.
Cut the white paper to fit on a curve inside the box to create the solid white background. i guess the is fabric diffuses the light and it seems to make the light less yellow.
I'd like to get some black paper and maybe a couple of other colours to experiment with what looks best with objects of varying colours.
