Thanks for your response. Here is one way color is being used. The intensity of the color red is used to indicate the intensity of the love interests across the various countries. Because there is only one numeric measure (love interest) needing to be encoded we address this with a single hue. Furthermore, since we’re talking about love it’s fitting to use the color red.

Thanks for your response. So here are one set of thoughts.
Different colors (or hues) encode the different races in this area chart. Race is an ordinal variable here, so we need to avoid a color ramp as well as any colors that grab stand out more than the others. We want the data to tell the story and color to simply support our ability to interpret the visuals.

Thanks for your response. Different colors are used to distinguish the cohorts. So the way we are using color here is to have the different green colored dots depict the changes between the two years. Importantly, when the difference is significantly greater for the same month, we use a darker green color, whereas a lighter green color is used when the difference is significantly less for the same month.