Hello,
This may have been discussed before but...
If you start out with a small file size .gif format of solid color and save it as an image, you can then open it in BV and stretch it to any size without a corresponding increase in electronic file size.
I have made a page with examples and samples free for the taking.
www.zone5pix.com/images-shapes.html
email (link on page) for a special request.