As far as I know, there’s no way to iterate through the columns of a table. One can only iterate through rows, so the data structure of the table that you’ve laid out isn’t the easiest to work with. The compiler certainly doesn’t understand it the way that you seem to intend, as can be seen by looking at the Index (under Contents/Tables).
I would recommend a table with three columns, structured like so:
Table of Mixing
previous new resulting mix
red red red
red blue purple
red yellow orange
red green brown
red orange red
red purple red
red brown brown
red white red
blue blue blue
blue yellow green
blue green blue
blue orange brown
blue purple blue
blue brown brown
blue white blue
...
[add rows as needed]
That way you can talk about the previous entry, the new entry and the resulting mix entry. For example:
Carry out pouring:
let C be the color of the noun;
let B be the color of BowlPaint;
repeat through the Table of Mixing:
if the previous entry is B and the new entry is C, now BowlPaint is the resulting mix entry;
if the previous entry is C and the new entry is B, now BowlPaint is the resulting mix entry; [checking reversed means fewer rows in the table]