A tortie/torbie based cat is either all diluted, or all non-diluted. The basic tortie/torbie types are:
(non-dilute types)
Tortie/torbie - the regular one, red tabby + black solid/brown tabby (brown tabby = tabby with black stripes on brown background)
Chocolate tortie/torbie - red tabby + chocolate solid (dark brown)/chocolate tabby (dark brown stripes on light brown background)
Cinnamon tortie/torbie - red tabby + cinnamon solid (reddish brown)/cinnamon tabby (red-brown stripes on beige background)
(dilute types)
Dilute (blue) tortie/torbie - cream tabby + blue solid (slate gray)/blue tabby (dark gray stripes on light gray background)
Lilac tortie/torbie - cream tabby + lilac solid (light grayish brown)/lilac tabby (light grayish brown stripes on gray/beige background)
Fawn tortie/torbie - cream tabby + fawn solid (light brownish/orangish beige)/fawn tabby (beige stripes on lighter beige background)
A mixed cream tabby/brown tabby cat isn't normally possible, because cream is diluted and brown tabby (as in, tabby with black stripes) is non-diluted.
This doesn't mean that you absolutely can't have a character with that coloring though - there's still a way.
If someone asked for a litter where one of the parents was part brown tabby and part cream tabby, we would assume that it was a chimera, i.e. two embryos with different genotypes merged in utero and grew into a single cat, which is what we usually assume for any otherwise-impossible color combination. This can and has actually happened irl (although it is rare) - under the spoiler is a photo of a cream tabby/black solid chimera cat.
However, if you breed a chimera cat, it only passes on one of its two genotypes. So it would either breed like a brown tabby, or like a cream tabby, but not both.
Alternatively, you could make the cat a lilac torbie, since it would be lilac tabby and cream tabby and lilac is visually kind of brownish. (I can't find a good photo of a lilac torbie cat but here's a lilac tabby so imagine that but with patches of cream tabby.) That would kind of keep a similar aesthetic except without the black stripes.
No problem, happy to help :)
