Generally white is usually the best to go for,
No it isn't. I have been present at loads of Christenings in C of E churches (both high and low church) over the years, and wearing white is definitely not a thing.
I agree that it is probably a recent "Instagram" thing, or perhaps a Catholic thing. White is such an impractical colour to wear with a breastfed baby anyway. Ignore advice to wear white unless you want to. It isn't a first communion service.