I am using Lovelace with stock day / dark themes.
So far a color of the “section”'s label was blue, I have some saved screenshots:
But a few days ago I realized that the color became black (white for the Dark theme):
Checked with an Inspector (Chrome), the label’s color is “–primary-text-color” (black).
I suspect that earlier the color was something like “–primary-color” (blue).