Hey mrsgerardway
I work at The Home Depot and have worked in the paint department for a good number of years, and, I'm an artist.
From what it sounds like the project that you are doing, I would recommend just using standard wall paint that you can find at any home center. The craft places sell paints in smaller and more expensive containers. You'd be better off using a low sheen (like eggshell or satin) interior wall paint you can find at any home center near you that sells them. As for us, we sell those paints in smaller quart sizes, or even 8 oz. test kits. Compare the size and price of buying tubes of acrylic paints at a craft store, it's a much better deal you are getting with wall paints.
To make sure that your orange, blue, and white blends in nicely, using a sponge is a great way to go! I prefer to use a natural sea sponge in this case, since it bounces and reacts to the paint and wall better than a regular man-made sponge. To blend it in, you can start with sectioning off the areas you know will work as solid colors for the orange blue and white. Depending on where and how you want to mix them, you can lighten and darken your colors as well by carefully mixing the paint with another paint. For example, if the blue is meeting the white, mix an equal amount of white with the blue to achieve an in between color and blend in, as this may help for a smoother transition.
To also help out, you can use a faux glaze if you would like to mix in with the paint where it is being blended. Glaze works as an extender, not a thinner, but it gives transparency in areas where you want the paint to blend in. It also slows the drying time down of the paint, giving you easier and longer work times with your sponge.
Finally, to get the best look to blend in everything, it really is up to personal experimentation and familiarity to get the results you want.
I would try a small area with all your colors first. Mix in the glaze you prefer (typically you mix 4 parts of glaze with one part of paint) to your wall and use whatever tool you would like to be the blended on the background. You can use a variety of tools in combination with the sponge, like a cheap foam brush alongside the sponge. But the key here is to experiment and get a good feel of how the paint and colors will react to the wall. That will be the best solution for what you trying to accomplish.
And after it dries, most decent interior wall house paints nowadays can hold up everyday trafffic since their formulas have additives like enamels that strengthen them. As long as you have a good primer or flat clean painted surface underneath, you are good to go with using a good wall paint alongside a faux glaze to get the background looking the way you want it to.
Hope this helps you out,
aboveaveragejoe