Yeah you're right. It's only a bit brighter from the darkest gray. There was no point of using it really now that I think about it. Thanks a lot for the tip
The second darkest grey you're using blends with the darkest grey zoomed out, so it's not really pulling its weight as a colour. You could replace it with the darkest and it wouldn't make a difference. Lightening it a tad might help, if you feel it's important for it to be a separate colour.
It's one of those things that looks like a fine decision when you're looking at a piece zoomed in. Keeping a 100% zoom preview open at all times and glancing at it regularly is a good way to avoid redundant colours like that.