Hi Julia,
You can update this in Site Designer. Go to Agenda Widget → Customize (right panel) → Session Filters → Filter Options, and change the text color to your desired color.
Note: This setting changes both the checkmark and the session filter text color. At this time, there isn't a separate option to change only the checkmark color.
Let me know if this helps!
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Sanjog Rana
Subject Matter Expert
Cvent Client Services
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