The `white_space` color theme setting can change the fore- and background colors of the dots to show spaces as well as the arrows drawn for tabs, if enabled. However, the setting is tied to both of them and my perception of the two is very distinct. In my usual setup I use 1440p 24" displays and the dots for whitespaces are actually a single pixel which is almost invisible for me with the default scheme while the tab arrows are quite clearly visible. I have played around with the `white_space` settings to improve the situation and ended up using a slightly grey background (`white_space=0x808080;0xf7f7f7;true;true`) which I am currently testing. However, I am not totally happy with that and it is just a workaround. What I would really wish for would be more pixels in the space dot to make it most distinct relative to the arrow. Maybe my setup is a corner-case combination of font size, monitor attributes and eyes but it would be nice if the dot shape could be changed in some way, which I think there isn't yet(?).
I have attached a photo of the situation with the default color scheme. It doesn't do justice to my perception where it is much worse but even here you can make out the arrow way better than the dots and I think it is easy to imagine that the dots get much harder to recognize when overall conditions deteriorate (e.g., the lens/eye is moved farther away from the screen). 