MM wrote:
I have several fine drying out cracks in the plaster of my house,
which is now about 18 months old. Several walls are affected. I shall
short;ly be placing the property on the market. I don't want to go to
all the hassle of painting all the walls, which are currently
magnolia.

My aim is to repair the cracks and dust over them with a fine brush
with magnolia so that the cracks are invisible. In other words, the
kind of repair done to Old Masters.

Possible?

Very hard (or impossible?) to do undetectably I'd say. If you're going
to do it at all, I'd paint the whole walls.

I could do this by colouring some Polyfilla to match the magnolia.

No way; you'd never get a colour match in a zillion years as the stuff
dries a different colour to its wet state. Likely to mess up the
Polyfilla setting, too.

Alternatively, just use Polyfilla as it comes, then brush across the
crack with magnolia afterwards. Maybe then leave it a couple of months
for normal ageing to work and for the newly applied paint to 'weather'
into the surrounding wall.

Use it as it comes; if you can find exactly the right paint (ie same
brand/type as used before, it might work. Otherwise it will probably
look like a bodged repair gone wrong.

It just seems a heck of a lot of work (and money) to repaint all the
walls, since the new owners will doubtless have their own preferred
colour scheme anyway.

Not an issue - the reason you are considering doing this is to conceal
the presence of the cracks from buyers, right? It's already painted in a
good colour (ie neutral/blank canvas) to appeal to buyers (Beeny Rule 17)

Another alternative is just to sell the house 'as is' and let them
worry about filling the cracks.

I'd do so, unless you're going to paint the lot. If it's all nice and
clean and you can get a good, albeit not precise, colour match, you'll
get away with a single coat for this purpose.

David