Hi Nathaniel,
The "problem" are
these lines in the default SnowWhite theme.
The SnowWhite theme uses a gradient for the tab buttons,
for which the colors are not exposed in the palette editor,
whereas I think they should be.
The thing is, separating "theme" from the "color-palette"
kinda pretends the two are independent,
whereas they really are not.
SnowWhite wishes to use gradients and Vanilla does not.
The only way to fix this is to have another setting in the palette editor
for whichever theme implements more fancy gradients, like SnowWhite.
Tip: If you switch to the Vanilla theme,
you won't run into this problem and get a proper contrast.