Back in commit 5dbd69486, I said:
> I'm choosing to use the same color for solid and hollow buttons
> because these elements are usually isolated and so from the UX
> perspective they are similar; links, on the other hand, are often in
> the middle of some text.
However, I made a mistake. The crucial factor is that solid buttons
might have a light background if we choose the brand color to be a light
one, and in this case they automatically get black text. However, hollow
buttons always have a light background and so we can't use a light color
for the text and border of these buttons.