For vision impaired uses that use custom High Contrast Theming, the Teams apps does not correctly map to the colors. For example, left list uses the Disabled vs Selected colors. Microsoft should be fully committed to one standard for Theming; especially for High Contrast Theme. It is critical for the vision impaired.
I apologize for being fairly ignorant on this topic. The color scheme setting can be found by clicking your portrait icon within Teams at the upper right. Under the General Settings you can select, Default color theme, Dark, or High Contrast. This follows the Windows OS high contrast theme and my understanding is also following the global standards.
If you are having issues could you let me know what exactly is happening or specifics you feel need to change? If you could tell me both and maybe even email me screen shots to TeamsML@microsoft.com I can work to see what I can do for you. Please list the subject in the email as “High Contrast”.
Sean Ellis commented
The contrast is not good. The scrollbars are not visible. You should be able to adjust the colors
Der Kontrast ist nicht gut. Die Scrollbalken sind nicht sichtbar. Man sollte die Farben einstellen können
(The current contrast is not good. The scrollbar is not visible. The color should be able to be set.)
Flat no-texture apps make my eyes bleed.