There is a fix for that. It is called interior cleaner.
Think about this. Those same stains you hate so much on light colored interiors, also exist on the black seats. But you choose to ignore them, because they don't stand out as much. After you think about that, isn't that just a little . . . icky?
There is another fix: don't wear blue jeans.
I don't get them: they're uncomfortable. In summer, they're hot and in winter they don't warm. The fabrik is rough, which means that if you walk a lot you will get rashes on you inner thighs (provided you are somewhat muscular) and they will wear through in a couple of weeks.
Dress trousers look much sharper, anyways. A heavier weave herringbone or even tweed in winter can be even be paired with boots without looking odd; in summer a leightweight wool is surprisingly cool. If it is really hot, nothing beats linnen.
And if I need something rugged or practical for the outdoors or if I am doing dome manual labour, I usually opt for bdu-style trousers. They don't stain, and if you buy quality they are almost indestructible (I especially recommend the Leo Köhler trousers that are based on the ansieht West german olive dran- but also available in other colours. That stuff is incredibly durable.)
Back to topic: I loathe black or dark grey interiors. Unfotunately that is 90% of what you can get here in Germany.
But what puts me off modern cars the most is the use of touch screens instead of buttons. Screens ruin night vision; they also require you to take your eyes of the road to operate them.
In that sense, most modern cars are less useful than oder cars. So what's the point then? Am I buying an ipad on wheels or a car?