I've heard that too but don't know in reality how true it is.
I've had a solid black bitch and a solid golden bitch. The golden girl (who I still have) has the best temperament in the world (except with other dogs
) She's fab with people especially children. She's almost perfectly behaved to the point where I swear she speaks fluent English - you couldn't hope for a more wonderful dog.
My black Sasha on the other hand had severe temperament problems. (Although I loved her more than anything in the world). She had epilepsy and spinal problems which didn't help, but she also suffered from rage syndrome. And I know of three other solid blacks who had the same. Sasha was very very sadly PTS (due to health not rage) in my arms 5 years ago and I still have the scars from where she had bitten me in the past. She was very affectionate, very loving and totally devoted to me for most of the time. But then she would go all growly and hunched up and a couple of seconds later she would launch an attack on whoever was nearest (usually me). It wasn't half-hearted either
! I had tetanus jabs and stitches several times. Afterwards she would be very disorientated for a while as if she didn't know where she was or what she'd done.
I think you need to be very careful where your new puppy comes from and that you discuss this issue with any breeders you approach. I am not saying that you shouldn't get a solid black bitch (they are my favourites after all
) But you do need to be careful.