While placing an error closest to the relevant buttons, the EuiCallout displaying the error was practically unreadable in dark mode:

This is impacting EUI version 34.0.0 (and earlier; we're on 32.0.4): https://codesandbox.io/s/wonderful-cloud-s3q62?file=/index.js

For anyone running into this issue, it can be worked around:

<EuiTextColor color="default"><p>...</p></EuiTextColor>