You set global colors in the Marketing Cards module, but nothing changes on your site. Per-card color overrides work as expected.
Why this happens. The global colors are applied, but the admin color picker layout can make it easy to configure the wrong field. In a narrow settings panel, the color swatches and their labels can appear visually offset from each other. For example, the Background swatch may sit right next to the Text label, so it looks like you are setting Text when you are actually setting Background. Also, if a card has a cover background photo with a dark overlay, any change to the Background color is hidden behind the image and appears to do nothing.
Per-card overrides read correctly because they use a different layout that groups each swatch with its own label.
What you can do. To confirm which color landed where, set the Text color using the second swatch in the global colors section, or temporarily remove the cover image to see the background directly.