Yeah. I was thinking the same. I'll start with grey since the rainbow has beel all used up If you feel some other color would be better, I can then do a new one, but this will give the first impression.
No that ain't transparent yet as I did that with MS Paint I think once I have my hands on a real program I can smooth the edges a bit (although I can already that all it needs is removal of few pixels..) and then make it transparent png.