They say you learn something new every day, and I’m proof that it still applies, even if you are an old duffer like me.

In the last week, for instance, I learned that although there are several colours that the sea can appear to be - blue, grey, silver and even green - never is it purple.

This is bad news for somebody like me who is colour blind but making an effort to get back into a hobby I have been neglecting in recent years, namely drawing.

For obvious reasons, I usually stick to black-and-white, but after successfully drawing a wasp (having established that everything about him is either yellow or black), I got carried away and had a go at drawing a beach in Tenerife, based on a nice photo I took on a holiday this year.

It was going well until I needed to choose a pencil to colour the sea in with, and because I am impatient but there was nobody in the house at the time who could advise me, I grabbed one that had ‘violet’ printed on it.

I was pleased with the result until my wife got home and broke the news that everything in the drawing that was violet (or purple, as she called it) should have been blue.

How was I to know that violet, which I thought was a shade of blue, is purple in disguise?

Colours like violet, purple and several others that also shamelessly masquerade as blue, such as mauve and lilac, are probably the most annoying of all, because to my eyes they are lots of different and confusing names for what amounts to more or less the same colour.

Although my wife usually thinks my colour blindness is a bit of a laugh, this time - bless her - she could see my disappointment, so tried to console me by saying David Hockney (probably the world’s greatest living artist) doesn’t necessarily use colours that are true to life.

As if his colours are an accident.

On the bright side: my drawing is nothing if not unique, and there is a moral to the story.

Even colour blind people can have a go at art, and if you had a go yourself, at least you would be starting from a position of massive advantage over some of us.

So what’s stopping you?

Although black-and-white will mostly be my limit from now on, I am far from being deterred. On the contrary, I am getting the bug.

As a member of the Swindon Urban Sketchers, I was due to visit John Lewis with the rest of the group at the weekend (I am writing this before, so I cannot be sure I didn’t chicken out).

It is quite a challenge to draw when people are looking over your shoulder, but if all went well, the plan is to return for the group’s contribution to Swindon Open Studios (SOS), the annual event that this year takes place over two consecutive weekends, starting on September 22.

That’s the date the sketchers and I will be doing our stuff at the Central Library.

The people running SOS have produced a brochure and a website with details of all the venues involved in the event this year, which run to an amazing 54.

If the beautiful brochure is anything to go by, it will be about quality even more than quantity.

Colours will always baffle me, but any fool can see that our town has far more than its fair share of brilliant artists.

So don’t be blue if you are an artist in Swindon. Our art scene is going through a real purple patch at the moment.