That's funny, I always thought 'Colorama' meant it was a rebuild but that base says 'all new materials'.
This is what my '59 21CYP22 looks like:
Perhaps all tubes beyond a certain date ('60 or so?) were Colorama, while earlier production ones had a base like mine?
I also have a trio of 21AXP22's. The one that was rebuilt in '65 and went to air has a blank black base (probably not rebuilt by RCA), while the good RCA Colorama rebuild lives in my CTC-4. The 21-CT-55 still has it's original tube in it with a similar base to the CYP in the picture, though the tube type is stamped on the neck not engraved on the base.