As requested in T90025, this adds a subtle mouse hover highlight when
selecting items in the Monkey 101 Template.
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Although task T90025 asks for "mouse hover highlight for UIList elements" the elements in question are `UI_WTYPE_PREVIEW_TILE`, which draw with a custom routine and so have to handle hover highlight (state of UI_ACTIVE) on its own.
This just makes the inner color have a slight blend with text color. Not sure if you want something different or less subtle, but this might be a start and something to test.