Six years later, seconding the white background problem. If you're worried about visibility, why not add some extra flair to the presentation, e.g. have a transparent background, but put each category of items within a box that has a solid background and a frame?

 Thanks!  But if I make it a colour other than white it makes it difficult to put a sprite together, because you can't use the transparency option in MSPaint.  Also, when I tried it out the white items were hard to see...  But thanks for the suggestion, I can see what you mean.  X)

 nice spritesheet, but i'll recomend you change the background for a colour softer than this, a pure wite like this makes very hard to aprecciate the details