I used iron-on transfer paper, printed out the designs I wanted, ironed them onto the canvas then painted around them. There is still a color difference when you reach the iron-on paper, but with enough coats it will cover it up.
10 Best Printable Transfers for Furniture – Free! The Graphics Fairy. This is a great collection of the 10 easiest Printables to transfer onto furniture. Great for adding some extra interest to DIY Home Decor and Decorating Projects!