What language mode is this for? And where is that token, in a string, in a comment, etc?
As a rule of thumb, if a language mode's color coding recognizes that entire token as a number, and we can evaluate it as a number, we should be able to make the tooltip for it, plus or minus some other details.
Off the top of my head, I don't know of any language modes that recognize a hex number without a prefix, because it can be ambiguous - is "ace" a number or an identifier? Maybe possible with a more limited data format where only numbers can show up in some contexts.