A lot of it of course has to do with what people fish with, and what they've been taught is best at different times of year. But none the less, the big, black tubeflies with lots of flash that I like to use in the spring are much less effective in late summer and early autumn. The same pattern can be good though, but in much smaller sizes (1-3cm sometimes).
But generally, people (and I) drift towards smaller flies in browns, olives, oranges, red and yellow, and personally, I find the transition difficult. The Danish rivers aren't clear as such, most have some colour, and I have no problem believeing that the salmon will see a 4 inch long, black tubefly with loads of flash! But believeing that they will wee and pick up a small, orange and brown 2cm long fly is harder, but still - they do!
A favourite the last 2-3 years has been the shrimp pattern in the picture, one I picked up from Davie McPhail's YouTube channel. I'm not sure if his an original of his, or someone elses, but it's a beautiful fly that really lights up in the water, especially if there's a little sun. It's one that I really believe in!
There's an interesting report online somewhere (and I can't find it right now of couse) that documents that some salmonids (not sure atlantic salmon is mentioned specifically) can't really see orange when they enter the rivers, but that they actually (re)develop the ability to see it furhter into the season, as they themselves change colour towards the browns, yellows and oranges. Which might account for the effectiveness of orange flies in the late season.
It's a complex subject, and there are so many exceptions that I'm not entirely sure that it really matters which fly you have on, but it matters to me, and I like to change flies according to conditions, tactics, my own mood (maybe the most important factor), speed of current etc.
I had a discussion with Bernd in the spring in the banks of River Skjern in Denmark. Bernd presented the idea that the slower the current, the more effective smaller flies are as salmon won't spot them as easily, and they're then forced to make a quicker "decision" on whether to inspect the fly or not, and I suspect he's right. It corresponds well with the effectiveness on very small flies on low (and slow) summer water in for instance Norway.
Right, I'm off to the tackle shop to stock up on leaders!
Have a great weekend!