Technically, yes, changing that value does affect what color is being chosen, although it does prioritize with other factors as well which will affect the decision (e.g. the amount of gems on the board). Changing this value though will change other factors of the game though. I wouldn’t recommend having any gems changed “all the way”, as this could affect all gems your AI will match, and will possibly take purple gems over something like skulls, or casting spells.
Just as a warning with the Gem Priority, this can greatly affect what gems/spells are chosen if picking the minimum or maximum. These sliders are better used for slight changes rather than all or nothing.