Hello Dimitris,
it sounds like your lamp is loosing pressure. Does your Manometer work properly?
It is also possible that your stainless-nozzle causes problems - this often happens. I would suggest that you check all led-seals by pulling the vaporizer and the rapidburner a little bit more tight into the ledseal.
Adding to this I would use a ceramik-nozzle, not the stainless one, as the negative effects are more than the positive ones while using the stainless version.
It also could be the simple problem, that just a little part of dirt stuck in the jet. Next time your lamp gets darker, just spin the handwheel for 360° quickly one or two times to clean the jet with the needle. This could be caused by your coloured fuel.
To clean your lamp, remove the vaporizer completely, separate its parts and place them in a cleaningfluid like Acetone or machine-dischalker (citone-acid) for several hours. After that blow out the parts by air-pressure and if needed, add some mecanical cleaning with a wire.
Good luck, Björn
Hi Dimitris,
yes, you can use paraffin-oil without any problems in your petromax.
It is even cleaner than kerosene. 
Good Luck, Björn
Great
Enjoy your lamp - that works most perfectly when you're sitting at the beach with cool beer and on sundown. Take some friends and make the following night your day! 
Always good licht, Björn
Hehe, a friend of mine works also for Berenberg - like i always mention, the world is a village 
Greetings to Athens, Björn
