Keep in mind that your leaven is a living thing. It’s like a pet, it needs to be fed. But, exactly what you feed it is your choice; it doesn’t have to be white bread flour. If you want to increase the depth of flavour to change the taste and characteristics of your bread, feed it with rye flour, or wholegrain, or mixed grain, or with a malted flour of some kind – it’s totally up to you. Remember though that it needs to be flour which contains gluten, so whilst you could add say, some spelt flour, don’t make all your feed spelt, as it may not activate properly.
Once you have something that you prefer, just keep on feeding with that type of flour as normal, and over time the flavour will develop even more. In time, post up what you’re feeding it with and lets see how you’re doing. Pics would be great – if you struggle to upload them, send them to the leavensent email address and I’ll upload for you.