Here should be all the info you'll need to follow if you want to make a crosscat! Remember that these are only roles you need to follow if you want this to be a following my concepts!
They come in all sorts of colours, but there's a few rules for patterns! Most importantly, there needs to be a cross on the back formed from a stripe down the middle and a line across the shoulders. Since these are *cross* fox and cat hybrids, all of them have crosses on their backs. They also do need a minimum of two colours/shades (this can be monochromatic with one darker and one lighter colour or something like that!). One colour for the cross pattern, and one for everything else.
Though the cross on their back is required, in modern day they can have any fur pattern. If you are creating a modern-day character, it can be included that they have bleached their cross/dyed it (though it has to be recognized that their natural fur has the pattern). In the wild, however, their fur patterns may have any fur patterns that appear naturally in cats and foxes (in addition to the cross). Most common is a cross fox fur pattern where the darkest colour is the cross and the lightest is where the red/white would be.