Hello Dennis from Holland.... I'm Tyson from London, so pretty close to you... welcome to the forum!
I smoke a lot of salmon in the Bradley, and I do get some nice colour on it, but of course salmon is already a nice pink colour so it's not a huge difference.
I guess my first question is are you leaving the top vent open when you smoke? You need to make sure there is plenty of airflow through the smoker, this will help to remove surface moisture from the fish.
Second point is to make sure you have a good pellicle on the fish.... it sounds like you already let the fish dry before smoking... but you can extend this even longer to really make sure this happens. This helps to form a sticky surface for the smoke to adhere to, and also helps to slow moisture loss from inside the fish to the surface.
Third point is that it may help to start the smoking at a lower temperature, like 100-120F (you'll get that using JUST the smoke generator without the main element) and then start the main heater and slowly move the temperature up to 160-180F to finish it off at your desired texture. There is a fantastic recipe for hot smoked salmon here:
http://www.susanminor.org/forums/showthread.php?105-Excellent-BRADLEY-Smoked-Alaskan-Salmon. You can ignore the recipe (or try it of course

but the smoking times Kummok gives will work for your trout. I would advise using the lower times and temperatures, since your trout fillets are probably a lot thinner than salmon.
Let us know how it turns out, and post some photos!