"He who marches out of step hears another drum." ~ Ken Kesey
I just got a newly designed gallon of Ulano QTX emulsion. It now has a handle and a screw on dispensing lip. Have not opened it yet and do not have a camera handy for a picture.
I haven't seen one up close and personal, but it seems that Ulano has felt your(our) pain.http://www.ulano.com/ProdFactSheet/Emulsion/EZ_Flo.pdf
Acording to "Greaves on garments" at Mindseye, hosted by Mr. Kitson, wet emulsion is not affected by light. It is only affected after drying. And even then, I think you could spray the plastic container with some paint to make it more opaque.