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Fun fact
I've heard people say that Lego invented tan in 1998 for Adventurers, but this isn't true at all. While the Adventurers line was the first extensive use of tan bricks, you may know that tan baseplates were used for the Western sets in 1996, and 1997 saw the first tan minifigs in the Indians subtheme and tan was also used for sand in the Outback and Divers town subthemes in the same year.
But the history of tan goes back further than that. The first use of tan as we know it today was in 1982 for loaves of bread in the Fabuland line. Tan 4x4 cones were also used as lampshades in a couple of duplo sets in the 80s and early 90s.
However, according to Bricklink, Lego made tan parts way back in 1957 in the form of 1:87 scale cars. I assume the plastic recipe would have been different back then so the colour wouldn't be exactly the same, but it's listed as tan on Bricklink. In fact tan has the colour code 2, larger only than white.