We follow the accessibility standards specified by w3c. The application can be enabled with accessibility features once you turn on accessibility at Access Group level and adding PEGA-WAI ruleset to production ruleset.
SKIN Level there is no specific dedicated feature for accessibility. Yes, colors and text sizes can be edited in skin with your organization standards of accessibility. Rest of the features like, tabbing, read out labels, instructions comes by default by enabling accessibility
The cosmos skin goal is to render the application in single web page application format, So, I assume that there is no specific accessibility features incorporated.
Hope this helps. Yet, you can shoot questions if any.