In this case, I had a beautiful overmarbled paper (on 140# cold press watercolor paper) that I thought I could perhaps turn into a painting. The circular marbling (a modified "tiger's eye" pattern) looked, to me, like hydrangea flowers, so I thought I'd try that idea.
I drew the vase and outline shapes of the flowers using water soluble crayon but everything was the same general color and value. Using acrylics, I painted teal in the background but that was too solid and boring, so after that dried, I used thin automotive detailing tape and applied it in striped formation on the teal. Then using a foam roller with off white acrylic paint on it, I lightly went over the teal section and then I pulled off the thin tape. It left a nice striped pattern in the background. I had some stenciled collage paper (on thin deli wrap) that I cut out for the tablecloth underneath the vase.
I used a white acrylic fine tip pen to scribble a pattern all over the flower heads. But the overall shape of the flowers seemed awkward and I realized I wouldn't be able to easily fix it since I'd covered up so much of the marbling with acrylic paint. I set it aside and then the next day, I went for broke and started dribbling paint and water spray on the painting, thinking I'd make it into an abstract piece.
But then I turned it horizontally and realized I could salvage a smaller bunch of flowers and shape it differently. I painted aqua onto the vase, glazed the hydrangea heads with orange acrylic (not a typical hydrangea color, but I've seen it) and then added a bit of collage paper on the middle/upper left of the painting to tie it to the collage paper on the right hand side.
Not bad for a painting I was about to give up on! By turning it, I was able to look at it another way and realize I could still create a vase of hydrangeas---different from my original vision. "Hydrangeas in Vase"; acrylic marbling on paper, 12 x 18".