This looks like an error with meshimage, which I should be able to correct in GeoMakie.
That being said, you can get around for this by now using something like:
mi = meshimage!(ax, -180 .. 180, -90 .. 90, reverse(rectimg[1]; dims=1); npoints=1000)
mi.plots[1].colormap = :jet
which works for me.
Also, you might use a perceptually smoother colormap like :turbo instead of jet, which is known to be misleading (see e.g. this article) 