Let us imagine a language with a gender or noun class system of some description. Now, let's imagine that usually, adjectives (maybe verbs too) have gender congruence with the main noun, but sometimes an adjective (or verb) will gain a different meaning in some gender markings, and this gender marking turns into a semantic marker - almost a derivative marker - for these lexemes.
Let us consider a system with a noun class for 'tools'. Let us imagine that due to metal object being quite hot when red, the adjective 'red' thus starts signifying 'hot' when dealing with tools. "red-tool" then becomes one of the ways of describing any hot object, and so "red-tool drink-comestible" means "hot drink", but "red-comestible drink-comestible" signifies a red drink.
This would be some kind of differential gender congruence. Let's consider onwards what happens when we want to describe an actually 'red' tool:
- We can make the distiction only be available in every other noun class, so in the tool-class, this distinction cannot be made using congruence as a tool. So, expressing 'red tool' requires something like 'tool whose color is red' or 'tool of redness'.
- We can even say the speakers don't care for the distinction, since differential object marking only is used in situations where the difference is not important for the particular class of things (i.e. all red tools are also hot when they're red, but for other things, 'hotness' and 'redness' do not necessarily coincide)
- We can permit the use of a default noun class marking (i.e. 'red.masc knife.tool')
- We can permit the use of zero marking (red knife.tool) to provide the default meaning
A few examples of potential meaning distinctions:
bad - with animate noun classes: 'evil', with inanimate: 'unfit, useless, no moral judgment implied'.
heavy - with feminine noun class: pregnant (also when used of non-human animals in their noun classes). Here, maybe using male gender for the adjective denoting heavy females could also be justified
talkative - signifies 'loud' when used with an inanimate noun class marker
angry - signifies 'dangerous' when used with an inanimate noun class marker