When creating a data card, the colors are auto assigned by default. You can customize the data cards by assigning different colors based on your preferences.
Bar, Horizontal Bar and Line charts
For these three Axis charts, once you select the config, click on the Style tab. You'll see the selected/configured axis listed under the Variables section with the default colors. You can select a color from the color grid based on your preference.
Donut
For donut, once you have selected the config, click on the Style tab. You'll see the values of the category column under the Variables section with the default colors. You can select a color from the color grid based on your preference. When the category column gets new values in the future, the colors will be auto assigned without overlapping with the existing colors.
The color of the sub category is a lighter version of the selected category's color.
When you configure a minimum value, by default Grey color is assigned to the "Other" category. You can change this color as well from the Style tab.
Gauge
For gauge data card, you can select your preferred color for the ranges. If the value in the selected column falls in any of the range then that range's color will be assigned to the value.
Metric
For metric, once you have selected the column, you can click on the Style tab, to select your preferred color. You can also optionally configure ranges and it's colors as per your requirement.
Funnel
For funnels we have color themes instead of individual colors. Once you have selected the config, click on the Appearance tab. You'll see the color theme picker under the Viz theme section with the default color theme. The color of each stage is calculated based on the selected color theme, from darker color to lighter color.