Hi Henrik,
Sorry, can't help with the colour but I wonder if you can use the following technique to clean the rust off your chrome.
Take a piece of aluminium kitchen foil. Dip it into vinegar. Stroke (don't rub hard) it backwards and forwards across a bit of the tank until the rust disappears. Wash the vinegar off with water and dry it. You can then polish with chrome polish.
The action is chemical, not abrasive, so don't rub hard. I've tried this a couple of times with good success. I'm a fan of keeping the original chrome and paint if you can.
Cheers
Leon