There are some rare pennies (cents) that are struck on the wrong planchets. A planchet is the little disk of metal that is prepared to be struck into a coin. Sometimes a mix-up occurs that causes the wrong planchets to be struck into coins for a certain year. In 1943, for example, pennies (cents) were supposed to be struck on planchets made of STEEL, and PLATED with ZINC. Some leftover planchets from 1942 made of BRONZE accidentally got mixed in with the new, at the time ZINC-COATED STEEL planchets and were mistakenly struck into coins.
That being said, many questions arise about the 1943 dated cents. You should know what is normal and what is unusual on these coins and coins of other years that may be struck on the wrong planchets.
NORMAL 1943 Lincoln cents are made of STEEL plated with ZINC. NORMAL 1943 cents are grey in color unless they are rusted.

1943 Lincoln Cent - Steel Plated in Zinc - NORMAL COMPOSITION
1943 P, D or S cents struck on BRONZE do exist but are extremely rare. This picture shows you the date on a genuine 1943 S Lincoln Cent that was struck on a Bronze Planchet.

1943 S Lincoln Cent - Struck in Bronze
Many are counterfeited. People take normal STEEL cents and plate them with COPPER in order to make them look like a cent struck in BRONZE. People also take 1948 dated cents and alter the date by removing the left side of the numeral 8 and leaving behind what looks like a 3 as the last digit in the date.

A copper plated forgery of a 1943 Bronze cent
There are some 1944 Lincoln cents that were mistakenly struck on leftover ZINC -COATED STEEL planchets from 1943, so a NORMAL 1944 is BRONZE colored while there are some rare 1944 cents that are grey in color. Again, there are numerous counterfeits done by plating a normal 1944 cent.
In 1975, NORMAL cents were struck in BRONZE. The Mint did experiment, however with ALUMINUM and struck a few examples dated 1975 in Aluminum but no coins in that metal were to leave the Mint. Samples of these ALUMINUM cents were given to some members of Congress as examples to examine and an unknown, extremely small number that should have been returned to Mint officials escaped but rarely surface. So a white 1975 cent bears further examination but is still probably a plated forgery.
Part way into 1982, the composition of cents changed so some 1982 cents are made of the traditional material which is a copper alloy (BRONZE) and some are made of a mostly zinc core that is plated with a thin layer of copper.
From 1982 to the present, cents are made of the COPPER-PLATED ZINC material. On occasion, unplated planchets are struck and a light gray colored coin is the result. They need to be carefully examined as it is easy to remove the copper plating and coins of this date range that have been tampered with are often encountered. High school science experiments use these cents and there are experiments done that remove the copper and the altered coins can end up back in circulation.
On a cent dated 1964 or earlier, it is possible to actually have a “silver cent” (remember that “white (light gray) cents” are normally steel or zinc and not really silver) . On rare occasion, a planchet intended to be used to make a dime gets into the press and is struck by the dies intended to produce cents. A true “Silver Cent” is the result.
If that happened today, a cent would be grey in color as our dimes (for circulation) are made of two layers of nickel bonded to a copper core.