Hello Eddiexero, I experience a (white) cloud affect when I dye vegetable tan leather with Fiebings’s black dye. No matter how many times I’ve cleaned it the “cloud” always appears. I apply the dye when the leather is dry. When the leather dye dries I buff it off and add a second coat and it goes away!
I too use an air brush and I have experienced those markings, which appear to have been splashed (or possibly a spit take) and a half assed attempt was made to wipe it off. If it came from fingers you would of most likely seen finger prints.
i sometimes use a dye-prep that helps clean and prepare the leather for dye. It evaporates rather fast and the dye must be applied while the leather is wet. To apply the dye prep you 1) rinse a sponge till the water is clear. 2) wring the sponge almost dry. 3) Saturate the sponge well with the dye prep 4) evenly wet the entire surface. 5) apply the dye with the surface still damp from the dye prep
one can also make a dye-prep (YouTube)
the more I look at that pattern, the splash could of been a bounced sprite or clear soft drink, a cough or maybe even a sneeze, and it is all possible because you have no idea where that leather has been or the abuse it received in just day to day handling.
Isopropyl alcohol leaves a faint residue where sugar will leave marks like what is displayed on your piece, been there - done that (Golden Retrievers help with all kinds of messes)
if a soft drink dries on leather it must be flushed with water to get it all off, just wiping it with a paper towel won’t do, thus it will look like what you have