The color is much darker when it is wet.
That's absolutely typical!
In a way it kind of looks like old wheat paste wallpaper paste residue which dissolves in water ... which I had many sq ft to contend with.... but I don't know if that would feel "chalky" more like a rough texture.
Technically the two are very similar but the paint has a lot of chalk and/or powdered clay in it so that's what makes it sticky.
As I scrub away, I ponder how they got the blue paint on top of the salmon paint - as it is very water soluble.
Painting carefully and quickly, possibly spraying. It can be done if you're fast enough, applying the fresh paint before the old coat has had enough time to soften. It wasn't recommended though.
I wonder if there are regional differences as to the appearance and behaviour of this paint due to varying recipes/manufacturers ? Was it sold dry and mixed by the user, or sold in cans like conventional paint today ? Does anyone know ?
It is often called "distemper" maybe its a regional thing with the name? I seem to recall being told it was sold in solid form (whiting) and mixed on site (addition of water, glue and color)
Apparently kalsomine/calcimine/... is the wrong name for what you're dealing with (as I just found on Wikipedia). Calcimine - as the name hints - is a plain whitewash consisting of lime putty and water. Distemper, or more precisely soft distemper is what we've got here, likely cellulose-based. One of the linked articles at the end of the page uses the two terms interchangeably though.
https://en.wikipedia.org/wiki/Distemper_(paint)
Distemper was either sold as a powder or mixed from scratch on site because it has a fairly short shelf life when wet - it gets mouldy. When my dad moved into his first apartment in the late 60s my uncle advised him how to paint, mixing clay, chalk and glue with water in different buckets, letting everything sit overnight and finally mixing the paint. The paint was then either brushed on or sprayed using old-fashioned pump sprayers, creating an INCREDIBLE mess, like any spray job. I've got one of those but it's broken, probably needs a bunch of new washers and whatnot. My dad tried one back then and didn't like it - he said you'd either get individual minuscule spots of paint on the wall or wet drips, depending on the consistency. I'm still tempted to try it myself.
In this house the original paint was likely casein-based hard distemper as it's really set on the plaster and requires lots of washing to get it off completely - on the other hand it's easy to paint over. I know for a fact that it was sprayed because they painted before installing the oak floors - every time you take up a floor you can see the overspray on the subfloor.