As rocketguy101 and Luke Strawwalker said, the color of the ET is the spray-on foam’s natural color (except for STS-1 and 2).
I suggest going to this page on my website, which shows a lot of ET details, including various ET’s:
https://homepage.mac.com/georgegassaway/GRP/Scale/ShuttleData/ET_photos.html
Below is part of what I wrote on that page:
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The first two ET's were painted white. After that, they have been the natural color of the foam insulation. The color of the foam varies a lot. The foam originally is much lighter in color. Both age, and especially exposure to sunlight, causes it to darken. Due to slips in launch schedules, some ET's sat in storage for a very long time, so they got even darker. Also, in some photographs the color may vary due to the exposure or lighting. The only truly really useful color comes from photos on the day of launch and even then it depends on the lighting, exposure, and film color sensitivity.
On tanks that look dark orange or rust, but also have lighter orange or yellow-orange places on them, what is that about? Two causes. One, where new foam was applied in places for various reasons. Such as building up the foam ramps that are along the right sides of the conduit lines. The other, where old foam was ground down or cut into for some reason. Only the outer part gets dark, like a "rind", so when the rind is cut away the exposed old foam is lighter in color.
More recent ET's, "Super Lightweight Tanks", first flown in June 1998, are even lighter. I do not know if the foam itself is any different, or if the ET's are being produced closer to the time of launch rather than being stored for a very long time. In any case, the tanks can have an almost butter-yellow color to them when they arrive, as seen below. When rolled out, they might look a little darker, but not much. The big thing is that being exposed to sunlight for weeks on the pad, the foam gets significantly darker. But the RSS covers a lot of the tank from direct sunlight. So when the RSS is rotated back for launch, the ET has a sort of a "sunburned look", the exposed areas are darker than the areas protected by the RSS.
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So, the “right” color really depends on what specific mission you are modeling. And if it is a mission since 1998 or so, some parts of the ET may be lighter/darker than others, due to the “sunburn effect” of most of the tank getting darker in the sunlight while other parts are protected by the pad’s RSS.
The ultimate scale model I built, was the only shuttle mission I ever saw launch, STS-47 in September 1992. On that one, the ET was more of a rust color. I simply used a cheap spray can of rust-colored primer which was a decent match.
Some examples below of various ET’s/missions.
Photo 1 - 1998 - first super light ET, on arrival at KSC
Photo 2 - same ET with STS-91 very shortly after arrival at pad, before RSS is rotated into place.
Photo 3 - Probably STS-91, not certain, shortly before launch. Note how much darker the ET is in most areas, due to the sunlight.
Photo 4 - STS-91 liftoff. Note how much darker the ET is in most areas, due to the sunlight.
I will post some other photos after this message.
- George Gassaway
