I can’t say without knowing the specific ingredients and solvents, but just in general.

Different ingredients used for coloring dissolve differently in various solvents. Unfortunately, colors that are not from single ingredients sometimes have to be made from ingredients that don’t dissolve well in the same solvents. Also, different solvents and ingredients are less shelf stable than others or react more with oxygen or light.

Generally, if you want to keep pigments, or anything really, from decomposing, you need to store them in the dark or a totally opaque container and in a vacuum or in a very well sealed container, preferably topped off with an inert gas, or at least not oxygen which is very volatile.

The alcohol or chemical smells usually are the solvent evaporating. Things that harden in without special additives or things like UV do so by the solvents evaporating. The quicker the solvent evaporates, the quicker the paint sets. Alcohol evaporates much faster than water, for example.

Anyway, the containers that cheaper paints come in, generally are not 100% air tight or light blocking. Often I put my paints and similar things I dont use often in a vacuum bag that you cam pump the air out of and store them in a thick, dark box.

Acrylic paint uses water as the solvent, not alcohol, so that’s probably not what you’re smelling. My guess would be the binder breaking down, which is why it turns into a thin fluid while retaining its color. Hard to say for sure without more details like a list of ingredients.

I have 2 lines of though to explain this, both going totally different ways.

I am not a chemist, and polymeric science is arguably my worst. so take everything with lots of salt

I do not know your sex (yes), but for the first one it maybe matters.

Humans basiccaly have best perception of greens. we have 3 kinds of cones (color detecting cells) and it is basically blue and green and a little redder green (it effectively works as red detector), and we percieve much better granularity in green color spectrum. also those who are female at birth are better at this (some source that i remeber said something in line of 10x more colors observable by females than males). so it is possible all kinds of dyes degrade, and wwith greens you are better able to percieve it. this is in theory testable by perfectly caliberated camera and lighting and displays, and measuring the pl response (doable in a lab setup).

more likely reason is dyes degrade. dyes are often organic (organic in sense of carbon containing) aromatic or more generally resonant structures designed to have absorption in specific ranges. the wavelengths they absorb the most, or reflect or transmit (as in allow it to pass) determines their colors. for example, our sun has peak emmision around green wavelengths, and life on earth evolved too roughly reject that (they absorb lower and higher wavelengths, if they absorb the most common, they probably die faster). if i remember correctly, organic dyes in paint often absorb the wavelength and then emit (resonance, the color being the resonant frequency) the light, so green dyes get the most common light (assuming the paint is applied on a surface recieving sunlight, if not, with leds for example, it is a bit bluer), and hence has a higher degradation rate. dyes degrade by general oxidation or any other chemical reaction, and that could also be possibly more likely on certain pigments as compared to others, and thegreen one just might be more reactive one. If pigment is inorganic, then it is whole different can of worms - whatstarting compound - lets say FeO (II), which may oxidise further (green -> brown) or something else.

Without much to go by, there are just so many possibilities.