[racket] White-on-black: how to change the green background when mouse is over an identifier?

Dear all,

I started to use DrRacket about one week ago. Everything is very nice up to
now, excepted for an  annoying small issue related to colour configuration.

I am using an inverted colour scheme: I am writing in white on dark blue. I
was able to set all colours excepted one: the background colour of the
ellipses that appear when the mouse is above an identifier. By default it
is light-green, and this renders the white text above it unreadable.

I also looked into the configuration file, but couldn't find anything. And
selecting "white on black" in the colour tab doesn't help as that
light-green colour is kept unchanged.

Can someone tell me how to change that colour?

Thanks,
D. Pieroux

PS: attached a small picture showing the problem.
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