When the sidebar, using vertical tabs, is dragged to be small enough for the Hide Sidebar icon to show up in the toolbar, it doesn't change from the default black colour. When the sidebar is hidden, the colour of that icon does change to match the colours of the other icons in the toolbar. This only really matters on websites wherein the toolbar colour is too dark for black to have the requisite contrast to be visible.
I've attached pictures and videos to show what I mean.
Sidebar showing, icon not very visible (or not visible at all):
Sidebar hidden, hide sidebar icon matches colour of other icons:
Video to show the difference:
I expect the icon to have the same colour as all the others in the tool bar. It's only a minor visual bug, but I figured it's worth reporting and I wasn't sure if this is something that's been reported before -- I tried searching, but I perhaps I was using the wrong keywords.
Version 0.99.129-beta (WebKit 619.1.11.111.2)
Sequoia (15)