I regularly use the simple HTML based platform offered by zerodha in trade.zerodha.com
I am NOT talking about Z5 or Trade Express. I am talking about the home page where you have got the omsesys based NSE NOW interface (simple html platform). Since you want a simple one, you can use it. The background is also white there.
If you doesnt like anything I think you could use same google finance and use call-and-trade to place order… it is even simple for investors… no black or white…