Having photography as a hobby sometimes yields pictures that can be used to create more pictures.  I decided to give up the no-lines approach for now (though it is a great exercise to learn how to make shapes – I was just really frustrated by what I was doing), do some pencil roughing, and then work one color area at a time.  First the tulips in shades of red, orange, and yellow, mixing some oranges as I went.  Next, the greens of leaves and stems, consciously determining the areas to negative paint later on, as for the flower petals.  Finally, the bowl.  Before the whole was done, I went back to each area and tried to create a sense of depth by deepening other areas and being careful not to touch the areas I had left deliberately white.