You might say I am crazy or wrong but lemon pledge on black denim works great. I do my bike with it and it has had no ill affect on the paint at all. It does darken it up a bit and makes it pop just a bit more while still maintaining that nice satin/flat black look.
I have been washing mine with a car washing soap that is spottless using that Mr.Clean car washing gizmo.
Then I dry it down with my leaf blower. (gets the water outta all the cracks & crevaces)
It has worked great for me for the past 2 years.
It's quick and easy. That's why I went with the denim black. I want to ride it, not idolize it with a sacrificial obligatory 4 hour wash and polish every weekend. But that's just me.