Provide more legible text colors.
Teams provides a limited palette of text colors and little thought appears to have gone into their selection; many of the choices result in illegible text.
I suggest reviewing the recommendations established by the W3C in Web Content Accessibility Guidelines (WCAG) 2.0 technique G18, "Ensuring that a contrast ratio of at least 4.5:1 exists between text (and images of text) and background behind the text".
Sean Ellis commented
Microsoft's own UI guidelines say that applications should respect the user's choice of fonts and colors, as set in the control panel.