There are many colours to choose from, but being period correct is important when it comes to reviving the cache that the w123 has.
If you are keeping the cream coloured interior, you really need to maintain a shade similarity on the external panels, or go for a completely contrasting colour.
Manganese Brown is a richer shade similarity while something like Citrusgrun metallic (DB874) is a striking contrast.
Cypressgrun metallic is another nice contrasting colour, and looks fantastic on the sibling TE - but again, it is a colour preference thing.
Bold vs understated.
Both will be eyecatching if well executed. Kudos for the bold colours offered early on in the model run. the late 70's solid colours like cayenne orange, incarot, mimosa yellow, caledonia green are all very 'rare' colours compared to the boring taxi colours.
China blue (DB934) has always been a favourite of mine on the w123, especially with a light interior like palomino. It's quite classy indeed.
After all, I think that is the desired effect also - to create a classy youngtimer look, and perhaps if you are sick and tired of looking at Brown shades, then the only way to really get away from the earthy tones is to turn to something completely contrasting....
signal red (yeah I know... but it is RED and RED ones go faster) 568A - circa 1987 looks great with palomino.
Believe it or not, Smoke Silver (a 1985 colour, quite rare on w123) DB702 looks very good on a sedan with a palomino interior.
(I took out 1st place in 2011 @ mb act club concours class award with a rauchsilber / palomino 1985 w123 280e)
Ultimately though, there are 2 schools of thought. Early colour schemes and late ones.
The early colours - the bright vibrant highly contrasting solid colours, and the late subdued shade variations which blend seamlessly with the interior colour.
Also, some other things dictate the overall aesthetics - headlights for example... early sealed beam round lights vs rectangular euros, or the round euros
bumpers... sorry euro bumpers it has to be on a w123....
deck lid badge option delete. Only if you have a 200 or 230 and you want everyone to think you have a 280e... otherwise leave it on. anyone with a TD should remove the hideous turbodiesel badge from the right side. it is disgusting.
300D is a nice badge to have.
No chrome wheel arch trims.
Colour coded hubcaps or Bundts - it's an originality thing. Personally If I were to do another w123, I'd look for some m100 hubcaps and have some wide steelies fabricated to 'fake' a stock look, but bundts are fine....
All time favourite colour scheme? Has to be DB406 Cayenne Orange with a Mahogany interior.
Very 70's. Orange & brown. Have a look at this:
https://www.flickr.com/gp/zipzamzerpople/v3B587/
80's look? has to be DB568 signal red and palomino or cream beige
90's look? DB269 Tourmaline green and a cream beige interior.
I deliberately stayed out of the darker red / cabernet colours as there are very few that look good on a w123. And they are a difficult colour to 'get right' on the panels. but.... if you want the dark reds pajett red DB587 is the one to go for and looks awesome with palomino or cream beige interior.
good luck with your choice - it is a difficult one as there are so many awesome colours on a w123.