Just wear something sombre and respectful (i.e. avoid white linen suits with a panama hat if possible), nobody cares if it’s black or not, and if they do then they being unreasonable anyway.
I arranged my own grandfathers funeral a couple of weeks ago, and the last thing on my mind when I spoke to people who attended was “oh, look at what they are wearing”, I was just grateful that they had taken the time to come and pay their respects.
It’s nice that you’re actually thinking about it though. I received quite a few phone calls from people asking “is it OK if I wear x?”. I hate all black funerals anyway, makes a grim day even more miserable.