Now that you have the overflows flowing good, the designs to silence them are generally the durso standpipe, the stockman standpipe, the herbie overflow and the beananimal overflow. Note that some of these are combinations of other designs. They vary mostly in the complexity of construction verses how silent it is. You can google them to see the specifics. By using a known design, you'll get a know result rather than trial and error.
If you don't like the white PVC pipe you can get PVC pipe in gray or black. It's more expensive though. Here is a link to one supplier. (offsite) -
https://www.savko.com/collections/pipe-and-tubing Other suppliers are also good. You can also get fittings in these colors.
I don't think I'd bother painting the pipe unless it's an eyesore. Sooner or later your going to find yourself cutting it and changing it to accommodate something else.