I don't have a hard and fast set of rules for the colouring, it gets a little convoluted if you want to be absolutely precise.
General nuts and bolts I used for the later cars came out of the car with gold, so are plated gold. A lot of small screws from inside trim etc are silver, so I did those the same. Then there are specialist spots where these rules don't apply. This may be because the bolts and nuts came as part of a completed assembly from a third party (SUs, Booster, Wiper motor, instruments etc for example) and are made on a case by case basis on what you have in front of you as you dissassemble them. The boot board screws are supposed to be antique instead of the normal silver according to John Schmidt (who seems to be very well informed on the subject of plating, he is a Electroplater by trade), and I think sometimes the little screws were chromed (Instruments, switch panel and demister plates maybe on the Coopers? ) Some items of the car are not bright silver, but are gun metal silver (or similar) for example the Lockheed Booster cases.
I am not too pedantic, but split the bolts out into silver or gold, and the platers are happy to work with a division in the finish without any dramas. My simplified rule of thumb to suit myself only was to put nuts and bolts and washers and sundries into gold, and self tapping and metal thread screws (and their little washers) into silver. Everything else was a case by case basis.
I always keep a box of 5/16 and 7/16 nuts and spring wahers to hand which come as silver in any case, so it may all go to pot once you start assembling and the new nuts are within reach

But the original bolts are all marked AJAX on the top with the special marks, and it looks good when it all goes together as a little piece of personal pride.
If you REALLY want to get anal, the bolts used on an english assembled engine are different to the Australian one, as the bolts came from an English supplier. They have a little recess in the center of the bolt. I like to gather these aside for the engine assembly, just to excercise the anal retentive side a little...