Here is one of my favorite background color effects using gesso and water color crayons. I love how it gives your background a pastell-y painterly look with little effort.
First I prime the page or canvas with a thin coat of gesso and let it dry. Next I just grab a watercolor crayon that seems to catch my fancy at the moment and with not much thought of where or how much I scribble on some color (now if you have a definite plan or design then by all means go ahead with that but I like the random look myself!) You can add other colors at this point as well.Once you have some color layed down then take a paint brush of your liking (or you can use your finger if you like to get messy!) pick up some gesso, a nice light amount and begin to rub into your color with the brush you will see that immediately the gesso blends with the crayons and gives a soft blended look. The gesso is a bit dry and sometimes does not give you enough time to blend a bigger area so I just add some water to my brush to keep it a bit workable, it doesn't take much water at all. The key to this media combo is to experiment. Be careful with the mediums you add over top of this because if it is a wet medium it will wash away your color (I use a mat spray krylon). You can keep adding layer upon layer and the color
just gets deeper and deeper! This is a journal page I just did for the art journal class I am teaching, using this technique. "Peace"