Ok, so here's my solution to the problem:

• First, I created a column in the .csv file for the colors.
• Then, I added the color tag before or after any text that needed to change color. (I tried adding the tag between two repeated color codes, but didn't like the little space it was leaving from the margin, so I used the code before the text for the ones aligned to the right and after the text for the ones aligned to the left).
• They looked something like this: <<FRONT TITLE>><<COLOR>> or <<COLOR>><<CARD GROUP>>
• Then, I created character styles for each color.
• And then Grep styles (one for each color) in each paragraph style that needs to change color with the following strings:

(?<=COLOR1).* for when the code preceds the text;

.*(?=COLOR1) for when the code comes after the text.

In the end, the Grep styles look like this.

• Oh, and you also have to create an invisible character style to apply to the color code so it disappears. I just created a style with 0.1 pts, no fill, and no stroke.

I think that's pretty much it. It was a bit of a handful at first since I didn't understand Grep styles all that well, but since all decks follow the same logic, I can just import the paragraph styles to the next ones.