Anyone ever seen a flat bladed Stanley with a reddish brown opaque plastic? handle? 

Probably an early Stanley Workmaster.

Not a Workmaster.
I misspoke. It's a Hurwood. Pat # 1839835 (the # didn't help).
The handle is a solid color. Rusty brown. Smooth with no ribs.
Similar in appearance to Google's Stanley UK models with blue handles.