6561 color resistors: (white bits)
On the first view, coming from VIC-II, the color amplitudes look strange. In other words: you can clearly see that VIC-I and VIC-II had different designers.
Btw.: one color here seems to be "special" again. Either by purpose or by mistake. This time it's not orange, it's red. When I change the cos value to get the target color angle value, also the red's color amplitude looks more reasonable compared to the other colors (esp. cyan which should have the same color amp.).
Amplitudes of bright colors should be smaller than those of non-bright variants and color burst.
The color amplitudes are not constant in the VIC-I, their amounts somehow follow the theory (see EBU color bars).
If I add the (compared to the referenced color burst weak) color amplitudes to the light colors' Y-signals, the max. signal levels are still within the tolerance (before clipping).
For the dark colors, you could double the color amplitudes and still are below the signal levels of the light colors.
Is there a hint on the die-shot, how and how much the color amplitudes are switched?
Having seen the luminance resistors of VIC-I, actually I expected separate color resistor pairs for dark and light colors. But maybe it makes sense to have just one set and amplifiy the signal afterwards. So a potential phase/amplitude error is same for both the dark/light color.
For the real amount of color amplitudes, I think we can only do much guesswork without having any measurement data.
Also there might be the addiitonal parasitic phase(/amplitude) shift, different for ODD/EVEN. Again, just guessing.
I don't have a VIC-20, so I can't do measurements myself.
In case someone would send you a VIC-20, could you (do you want to) measure it?