Hi eDAD,

I hope you are doing well!

I am afraid that presently the Telerik UI for ASP.NET AJAX suite does not offer a skin that fully satisfies the sufficient color contrast requirement for WCAG 2.1 since this not only differs from the initial design of the respective skins but also would require a considerable redesign and introduction of breaking changes in the customers' projects.

Even the high-contrast swatch available in the Theme Builder app, which is developed with the idea of accessibility, does not satisfy this requirement.

The available approaches are:

• Construct your own skin in the Theme Builder with the desired colors which pass the validation criteria.
• Customize the skin you'd like to use to pass the validation criteria, e.g. register the external skin files and modify the colors manually - https://docs.telerik.com/devtools/aspnet-ajax/styling/controlling-visual-appearance/modifying-built-in-skins, https://docs.telerik.com/devtools/aspnet-ajax/knowledge-base/editor-registering-an-external-skin-of-radeditor or https://docs.telerik.com/devtools/aspnet-ajax/controls/scriptmanager/cdn-support/custom-cdn-provider#custom-local-cdn-provider. 
• Overrides just the CSS classes responsible for the colors:
  
  

  <style>
      .RadCalendar_Silk .rcTitlebar {
          border-color: #cdcccc;
          color: #0D707E;
          background-color: #e3e3e3;
          background-image: none !important;
      }
  
  
  
      .RadCalendar .rcOtherMonth a, .RadCalendar .rcOtherMonth span {
          filter: alpha(opacity=1);
          opacity: 1;
          color: #0D707E;
          background-color: #e3e3e3;
      }
  
      .RadCalendar_Silk .rcSelected a, .RadCalendar_Silk .rcSelected span {
          color: #ffffff;
          background-color: #0E8195;
          background-image: none !important;
      }
  
      .RadCalendar_Silk th, .RadCalendar_Silk .rcWeek th {
          color: #0D707E;
          background-color: #e3e3e3;
      }
  </style>
  <telerik:RadCalendar RenderMode="Lightweight" ID="RadCalendar1" Skin="Silk" Width="100%" EnableAriaSupport="true" EnableMultiSelect="false" EnableKeyboardNavigation="true"
      ShowColumnHeaders="true" ShowDayCellToolTips="true" SelectedDate="08/10/2015" ShowRowHeaders="true" runat="server"
      AutoPostBack="true">
      <FastNavigationSettings EnableTodayButtonSelection="true">
      </FastNavigationSettings>
  </telerik:RadCalendar>

  
  

Regards,
Rumen
Progress Telerik