To ensure that all text in the widget is legible, we automatically darken or lighten the event title text based on whether we expect the background to be a light or dark color. Because our widgets allow you to customize the transparency of their background, we cannot tell the effective background color, which might be determined by the wallpaper.
Therefore, we make an educated guess to the lightness of your background by looking at the "Event text color" setting of your widget. We assume that when you choose a light color, the event text should be light. Conversely, when you choose a dark color, the event text should be dark.
The red color you have set for the "Event text color" setting is considered a dark color, which causes the relatively light green of your event to become darkened. If you set a lighter color for the "Event text color" setting, the event text color should be shown as in your original screenshot.