The first brochure appears to be from 1961.
I found the following information from an ad appearing in LIFE Magazine, November 17, 1961 pgs 8-9.
The ad begins with:
"After 16 years of research and development Zenith quality comes to color TV"
<PICTURE>
The first set pictured in brochure number one is the same set pictured in the ad.
The following description is found below the set in the ad.
"The Bellevue, Model 6040 with Zenith Space Command remote control TV tuning.
Distinctive Danish Modern styling in genuine walnut veneer and solids.
Zenith color TV comes in your choice of 10 magnificent models."
The ad can be seen at:
http://books.google.com/books?id=6FMEAAAAMBAJ&pg=PA8