A good rule of thumb is bright day, bright fly and dark day, dark fly. In the case of pike flies bright meaning very flashy and dark meaning less flashy. Think about it from the pike’s point of view and it will make sense. A bait fish such as rudd or roach has scales which act like a mirror as they change direction and the sun reflects off their scales.
So a bright day it will be natural for a pike to see bright flashes of silver, gold or bronze. Whereas a dark day a darker dull silhouette would show up better for the pike and also appear much more natural to them. Some days pike will literally take anything you throw at them but most days are not like that. And sometimes especially in winter the right size and right colour can make all the difference between landing a couple of pike and blanking. So it is essential to have a few different flies in different sizes and different colours.
All our flies are tied on 4/0 timeco hooks.