There's this show back from 2006, starring Tomohisa Yamashita, that's called Kurosagi. It means "Black Swindler" in this context, but also features people called shirosagi and akasagi, meaning white and red swindlers respectively. It's also a play on words, as "sagi" also means 鷺, or egret. For those of you who live in the blistering cold places (i.e. north of Florida), that is a type of bird similar to a heron. It's long-legged, and cool enough, you can see that reflected in the kanji. But anyway, I just found out that a white egret is called a shirasagi, not a shirosagi. I wonder why that is, and why the show didn't go with that instead of shirosagi?

Well the readings for 白 are [小学]ハク、しろ、しら、しろ（い）[高校]ビャク [準1]…せりふ、あき（らか）、もう（す)
So that would be why its Shirasagi. If I recall correctly, shira is the old pronunciation, so you only really see it in compound words. Like a white lily is a 白百合, しらゆり.

As you why the TV producer used it? I dunno.