There's a recent class on here with Lea McComas using dynaflo fabric paints. You use a water soluble resist on the drawing lines. This is the class thequiltshow.com/learn/classrooms/category/latest/lea-mccomas-contemporary-batik . She explains it all well and your drawing is already done you're half way there.

I've not tried oil pastels, perhaps when I have a few pennies ......

I have used Cray-Pas, Oil Pastels from Sakura on several of my applique quilts to add dimension to my subjects. I make a paper window (cut out the shape of the area where the color is to be applied in a piece of paper). Secure the paper window to the quilt or block using pins or tape. The area to be colored can also be taped off using Painters Tape (depends on the surface and how easily the tape can be removed later) Rub the oil pastel on a paper plate - the colors can also be blended. Using a 4" x 4" piece of muslin, fold it in half and wrap it around your finger, rub the oil pastel on the paper plate and use the tip of your finger to apply the oil pastel to the fabric surface. Be sure to rub from the edge of paper window toward the fabric to be colored to ensure the color stays where you want it. Once the color and the effect wanted are on the fabric, cover with another piece of muslin and press with a hot iron to set the oil pastel.
Good luck - hope this helps

I found an old wall quilt I made with checkered spheres and it was based on my son's drawing. I colored the white checks with some kind of pencil. I can't remember what kind but it looks like regular art coloring pencils. It looks drab and I wondered if anyone can recommend paints or markers that would be more bright but easy to keep from bleeding out of where you draw. Thanks, Jan