Color of Aircraft Drop Tanks.

You can do some variation in tone, especially on veteran combat aircraft. A well weathered aircraft could have newer tanks due to older ones being jettisoned in combat. Or vice versa, older painted or bare metal tanks could be seen on aircraft wearing a new paint scheme recently introduced. The sway braces should match the color of the pylon carrying the ordnance item. But they often have the tensioning pads that are a natural metal of one type or another. 

Have a look at photos of the aircraft that you are interested in modeling, and you can often find examples.  

One important question would be the era, another the country.

Hello!

Researching my 1/72 A-4B Skyhawk, that was to be painted in the VFA-15 Valions scheme, I have noted that they have lovefully painted the squadron colours on the otherwise white tanks. That would suggest that the squadron didn't see those large drop tanks as a pure "throw-away" stuff. So as it usually is, a question like that shouldn't be solved theoretically, but you should rather try to find photos of a specific aircraft you're modelling, and those photos usually surprise you and can give you a lot of really cool modelling ideas. Good luck with your build and have a nice day

Paweł

Some examples of different drop tank schemes from the carrying aircraft. The F6F and F-18 have tanks from the older schemes. The F-4s look to have crossover solid gray tanks from the later scheme

RCAF Sabres in the three colour camo in Europe had drop tanks in either natural aluminum or they were painted PRU Blue.  Either way, the pylons were painted PRU Blue.