Have you noticed how many hair-dye adverts there on television at the moment? I don't know if there have always been a disproportionate number of hair-dye adverts, or if the SABC channels are offering special rates for hair-colourants, but every time I look up from my glass and reluctantly focus on the screen there seems to be another hair-dye advert shaking and preening and combing itself in loving slow-motion.

And once you have noticed them, you carry on noticing them, until they seem to swarm across the airwaves like a cloud of midges on a summer's afternoon.

I can't honestly tell you whether all the adverts are for the same brand or whether there is a marketing war between various hair-dye companies.

Like most sane people I don't pay all that much attention to the finer points of hair-dye advertising, but unlike most sane people, I do suddenly find myself lying awake at night, asking myself questions about the hair-dye industry. Whence this sudden glut of adverts?

Sex and the City was never meant to be a long-running show

Can there really be that many women out there clamouring to dye their hair startling shades of red? And if so, where do all these walking postboxes live? I have taken to lurking in public places with a clipboard, taking an informal census of red-headed women.

I can't say I have noticed any significant increase in perambulating redness, but I suppose it will take some time to build up a data base for purposes of meaningful comparison.

My friends have tried to steer me away from the subject of hair-dye adverts. "It is not healthy for you to be obsessing about hair-dye adverts in this way," they say. "Forget about hair-dye adverts already. There is no future in hair-dye adverts."

And I suppose they are right. So instead I turned my attention to Sex and the City this week (SABC3; Wednesdays; 10pm).

At first I thought I was watching another hair-dye advert. There was Sarah Jessica Parker, whom most people know as Carrie Bradshaw, but whom I know as one of the second-rate American actresses appearing on a range of hair-dye adverts.

To watch them now is to watch the twilight of the gods

I think she's the one who says she dyes her hair "because I deserve it!" Although that might be someone else. Perhaps it was Heather Locklear, or Julia-Louise Dreyfus from Seinfeld.

One day, all these actresses who appear in hair-dye adverts will be as well-remembered as that girl who played Laura Ingalls in Little House on the Prairie, or Audrey Landers.

Watching Sex and the City, it occurred to me that the gals would be well advised to do as many hair-dye adverts as they possibly can before it is too late. I don't know what happened between last year and this year, but suddenly it has become downright painful to watch the show, in the way that it was painful to watch Muhammad Ali carry on fighting into old age, believing he was still as fast and as pretty as he was when he was king.

Sex and the City was never meant to be a long-running show. Where once it spun a kind of dizzy dream of being adult and free in a big city - a dream so seductive and so heady that it could overcome any personal irritation with the characters themselves - there is a feeling now that is similar to that feeling that comes over you in a big city when you have spent the night awake and in a happy daze, but the sun is rising and the faces of the people around you look grey in the natural light, and you know that yours does too.

One of the attractions of the show - if, like me, you were one of those viewers who did not watch it for the summer frocks and the Manolo Blahniks - was the attraction of seeing characters, purporting to be drawn from life, faced with such vistas of personal choice and the consistency of character to continue making those choices.

There was something deeply attractive about the fictional world of a fantasy Manhattan, in which - just as in the even more overtly fictional Seinfeld - life seemed to be made up of an endless series of decisions about trivialities.

Everything in that fantasy world was a question of personal taste - a question, more or less, of style - which is profoundly alluring to those who live in a world that seems more impersonal and gives us rather less choice.

If the Manhattanites on these TV shows could spend so much time agonising about whether to date a man who cried after sex, and if they could spend so much time having lunch and debating whether or not offering oral gratification qualifies as putting out on the first date, then clearly they must inhabit a world in which those are their largest and most pressing problems.

That is the essence of glamour - a world in which all the politics are personal and the world itself is just a backdrop to your own crises of style.

Even though you know such glamour must be a fantasy, it is a fantasy difficult to resist.

Critics have long said of the show that the gals are not so much gals as men in drag. They were too sexually adventurous, too ready to compartmentalise their lives and deny the overwhelming primacy of their emotions to be convincing women.

For me, that is why they were attractive, even when they were irritating - they lived their glamorous lives with a power and a confidence and a disregard for the consequences that made even men wish to be them.

This season, they have been brought back to the real world. This season, their actions have had consequences. To watch them now is to watch the twilight of the gods - glorious, reckless creatures growing old and lonely and regretful, with their choices narrowing. As they would in real life. This is probably the most realistic season of Sex and the City.

Which is why it will be the last.