I don't have blue background, but my tank is in the middle of two rooms. So I clean half of my tanks backside, one end and the front. The rest of the glass I never clean, I just let the purple coraline hide everything. every 2 or 3 days I run my magnetic cleaning jigger over the whole thing to thin out the brown "dust". Then about once every few weeks (or when company is coming over) I grab a new utility knife blade and scrape the glass clean of coraline.
I went with glass just for this reason and a few others, cleaning and not worrying about scratches. BUT My tank is easily accesible from both sides so I can stand on both sides. I have a 29G that isn't so easy, but that one sits low and I can stand over it easily. That one I scrape maybe once a month just to let the natural sunshine in.
Either way, if you plan to scrape the back, pre-plan it and in mine, the parts I scrape the rocks are at least 6 inches from the glass (so I dont cause avalanches)
If you like blue so much, why not just let the back grow purple, or whatever and light the tank with 20Ks or actinics? maybe just suplimental 10K PC's to see all the color on occasion?