No worries at all!
An all-white cat technically has another color underneath all of that white. Think of it like a bucket of white paint was dumped all over a cat - they have the gene to be all white, but they also have genes for other colors hidden underneath! So your character could be any color, such as black or blue or red tabby etc., just with the Dominant White gene masking it.
Here is a litter for Petal with randomized parents that could have produced that color!
Sire: SH blue w/ low white
Dam: SH torbie w/ high white (carrying dilute and solid)
Toms can be black, blue, black tabby, blue tabby, red tabby, or cream tabby
She-cats can be black, blue, black tabby, blue tabby, tortoiseshell, torbie, blue tortoiseshell, or blue torbie
- kits will be shorthaired
- kits will have low white or high white
- kits can have any realistic eye color
- red tabbies will mask black or black tabby; cream tabbies will mask blue or blue tabby
- non-dilute kits will carry dilute; tabbies will carry solid