Steve,

Prior to Emerson's purchase of DuMont's TV receiver division in 1958, DuMont Labs also marketed color receivers under their name using an RCA chassis. Picture below is from Steve McVoy's web site.

Philco tried to manufacture their own chassis in the '50s but had problems with it and stopped production after only a few sets were made. Then they switched to an RCA chassis.

If memory serves, 1961 is the year Zenith manufactured their first color sets, followed by Motorola's re-entry in '63 after a 7 year absence. Both Motorola & Zenith always designed and built their own chassis.