Blazons are ideally as succinct as possible. Presumably, it's obvious what a thing looks like in nature, so you don't have to describe it further than that. It also makes room for hues that don't have heraldic names, like the particular orange in a calico cat's fur. You could try to blazon something like a cat couchant sable, argent, and tenné, or you could just say a calico cat couchant proper and call it a day. ("Couchant" = lying down; "tenné" is the name of a stain rather than a traditional color and can be interpreted as orange, dark yellow, or brownish.)

That said, you can get more specific if the appearance of a thing proper is not obvious, and anyway, some coats of arms are very complex and require very detailed blazons, so the blazon can be as long as it needs to be. For specificity, yours could go something like this:

Sable, an open book with cover proper and pages argent charged with writing of the field.

"Of the field" = same tincture as the field, in this case sable, so basically white pages ("argent" can be interpreted as silver or white) with black text. It's considered poor form to repeat the name of a tincture, so workarounds like this are used when needed.

~Neshomeh