kitten colours

Question
Hello,
I have two British Tipped cats. Male is a black tipped and mother was bought as the same but developed some tortie tips on her coat as she matured. The female has had four kittens which look like 2 female silvers and 2 cream males.
Someone has told me that my cats cannot be pedigree because  it is genetically impoosible to produce kittens of this colour from such a mating. I bought them in good faith and am now wondering if they are just posh moggies, as i know absolutely nothing about cat genetics! It makes no difference, as i love them to pieces, but am rather intrigued now!
Thanking you in advance for your expert help.

Answer
Hi sara
The colours could be genuine if the female was tortie carrying cream, but in order to be sure about the actual nature of the litter you would need to know the precise pedigree of each cat.
Ask the previous owner to provide you with the pedigree of both parents and then see if they were black carrying white or cream.
If they were then the colours are possible.