1928 D 1c Improper Alloy Ratio?

To clarify - brass is an alloy of copper and zinc in the approximate ratio of 66% copper to 34% zinc, so it is not comparable to the composition of a Lincoln Cent of this era with a ratio of 95% copper to 5% zinc and traces of tin.

This coin's color is a bit unusual, but not well within the vast array of commonly-seen examples.

Yellowish colour is most likely from environmental tarnishing/toning.

Based on the fact that the devices that have been effected are flattened, you can assume it was environmental damage that caused this.

Zinc has about 20% less density than copper, so an alloy with more zinc and less copper would weigh less than one with more copper and less zinc.

Since your coin has a normal weight I don't think it's coloration can be attributed to an increase in zinc over copper in the alloy, assuming the physical dimensions (diameter & thickness) of the coin are normal as well.

It's possible that the mixing of the metals in the alloy is the error, per the link supplied, but I'll leave that determination to better minds than mine.