I want to tart our kitchen up until we replace the whole lot in a year or 2 by painting the walls.

The units are off-whitewhite, the worktop is fake white marble, as are the floor tiles so its all a bit off-white.

Would I be better off going for a darker neutral colour to make it look nicer (thinking a bronzey brown / mocha kind of colour, possibly a bit lighter but not magnolia light)?

Would Olive green look horrible?

Are there any good rules on what colours to go for with a light bototm half?

The wallpaper is embossed so if one colour would hide this more effectively than another that would be useful to know.

Would Olive green look horrible?

depends on how dark a shade of green it is.
i did the same last week to our kitchen
units are a similar colour but the floor tiles are a brownish looking terracotta colour
we eventually went for magnolia for 2 walls and pale brown for the other 2 walls
the magnolia looked a bit pale so i ended up mixing and half used tub of dulux buttercream with gave it a creamy yellow colour
the brown we got was a coffee colour but once it went on it looked like poo so i mixed another half used tin of dulux cocoa brown
the finished look is now a cross between biscuit and caramel and looks really good.
just be aware that some colours dont actually look the same as they do on the tin so apply on a small section of the wall first to see what it looks like when dry

Samples it is then…

I wondered if there were any colours that would be more effective (or not) at showing up the embossed wallpaper.

depends on how heavily embossed the wallpaper is. also a gloss finish would show the contours of the paper more effectively but any imperfections in the wall would also be more apparent. we used matt finish